Probably the most commonly taken heavy support choice in the Dark Eldar army, its weapon loadout comes in two flavour, dark lances or disintegrator cannons. The wording in the codex is such that you can take any combination of these two weapons. I don't think I've ever seen a list where the weapons are mixed however, and that's down to one reason, synergy.
Dark Lances are specifically intended at killing vehicles, and although they are better at killing lighter (AV10, AV11) units, the lance rule means that you make AV13 and 14 much less tough. That being said, if you do run out of tanks to shoot at, a dark lance does a passable job of taking on infantry and monstrous creaturs due to its high strength. this is strictly a secondary option though.
Disintegrator cannons however specialise in targetting heavy infantry, especially terminators. their high rate of fire and low AP means that if you get a terminator unit in their sights, take aim and enjoy yourself. the comparatively low strength of a disintegrator means it's of little use against vehicles however, and so a mixed weapon loadout really doesn't synergise well.
Ravagers get a nice long list of vehicle upgrades to choose from however, so let's have a look at those too.
Shock prow: I wouldn't even consider it. the longer range of the weapons on the Ravager means you'll pretty much want it to be sitting in your backfield and not ramming other tanks with it. This is bad synergy!
Torment grenade launchers: These provide a nerf to your opponents's leadership, but at an incredibly short range. Synergistically speaking, the only time it would work is if you're looking to break an enemy unit that's made it into your deployment zone and is threatening the Ravager itself. Again, doesn't synergise particularly.
Enhanced Aethersails: These allow vehicles to move an extra distance, at the expense of shooting. Synergistically therefore, for a vehicle that has no transport capacity and is there purely to shoot, it doesn't work well. This is exacerbated by the fact that Ravager can shoot all of their weapons even if they move 12".
Retrofire jets: Do you really want to deep strike your Ravagers onto the table and waste at least a turn of shooting? This option simply decreases the damage a ravager can do and so doesn't synergise at all.
Chain snares: These have some synergy with torment grenade launchers, but in the Ravager's case, you don't want to be that close anyway, so again it synergises poorly.
Grisly trophies: On the face of it, as before the short range of the effect doesn't appear to synergise well with the Ravager sitting at the back of the table. Think again though, and you'll perhaps realise that if one of your units should fail a morale check and fall back, the Ravager is fast enough to get close to them to allow them to re-roll any other failures. It's definitely a luxury, but for its cost if you've got the points to spare, it may keep a unit on the table for you.
Envenomed blades: Petulant at best, taking envenomed blades assumes your vehicle is going to get charged at some point, and once again as Ravagers have extreme mobility whilst maintaining maximum firepower, this shouldn't happen to you very often. No synergy at all.
Night Shields: now we're talking a bit more. Granted, the Ravager is at least immune to bolter fire unlike the raider, but this does allow you to trade fire with similarly ranged units without too much fear of retribution, and can really scupper anyone carrying a multi melta.
Flickerfield: Under 5th edition this was a gimme, you just wouldn't see Ravagers without them. Now thanks to jink they're less common, and at 10 points the upgrade is relatively costly for its usefulness. But on those occasions when your opponent pulls out the big guns early and gets the first turn, even a 1 in 3 chance of saving the damage is good odds!
Conclusion: The ravager is one of the most common sights in a dark eldar army, but its options leave much to be desired. In particular i feel some kind of upgrade to allow '1's to hit would be well used, and I'm sure if that made the guns count as twin-linked you could bump the cost of that sort of upgrade and still see it taken regularly.
Not used this guy before, but here goes.
Looking at the profile, clearly the main focus of the model is close combat. As a monstrous creature however, it counts as relentless and so can fire its twin linked splinter cannon to full effect. As an aside, this is the only model i can see that gets a decent twin linked weapon in the entire DE codex (razorwing gets a twin linked splinter rifle, but who doesn't upgrade that to a splinter cannon?) The gun is largely a distraction though i think, and is far more use as something to do whilst getting into contact rather than the main use.
Extra close combat weapon: Duh, yes please. Combat unit with only one combat weapon? I think i'll take the extra one. Good synergy.
Twin-linked liquifier gun: Is not a close combat weapon, so removes that extra attack you've just got for taking a second. As a template weapon it does have good damage potential though, and when you're generating D6 attacks, doing a bit of damage before you get into combat doesn't seem like a bad idea to me, so I'd say that although it reduces the direct damage you're likely to do, the damage it can create in other phases means it does synergise relatively well.
Ichor injector: Best used when taking out lower toughness models, it's cheap enough to give it a go if you're looking to make points up, but given the Talos' strength, the models it works best against are more likely to be suffering instant death anyway. As such, it synergises reasonably with the purpose of the unit, though unless you really can't find anything else to spend points on, I'd leave it at home.
Chain flails: Definitely synergises well with this unit, D6 attacks is great, but to roll 2D6 and pick the highest means you're much more likely to be able to rely on the Talos to do some damage (think of it as a kind of fleet for combat).
Stinger pod: Decent enough against most things, the stinger pod is a throwback to the previous codex, but against toughness 3-4, poorly armoured units (ie other dark eldar, Imperial Guard etc) it should perform better than the splinter cannon.
Twin haywire blaster: On the basis that you can never have too much anti vehicle in Dark Eldar lists, this weapon makes sense. Problem is it's only ever going to help other units really, you can't rely on rolling a 6 for your haywire, so you're only really going to take off one hull point at a time, and it then restricts your assault to the unit you shot at, so I'd say it's not got the best synergy.
Twin heat lance: More like it, the heat lance at least has the potential to bust open a transport so you can charge the soggy stuff inside, but the difficulty is in getting it close enough to work its magic. It does synergise with the purpose of the Talos, but you need to think about what tactic you're going to use to get it that close.
Conclusion: The Talos is definitely a close combat orientated unit, and the options tailored to this phase of the game synergise well. Caution must be exercised however when thinking about its ranged armament as these combine less well with and can distract you from its primary purpose.
Yes, it's a monstrous creature. No, it certainly isn't meant for close combat. It has a split personality however in terms of its weapon options. Its basic armament is the spirit syphon, which is a template weapon. So problem number 1 is that we've got a shooting unit that has a weapon range small enough to mean that it will be in charge range of anything it's shooting at. And what that means is that your opponent can chuck a cheap unit at it and reasonably expect them to bog it down in combat. Its basic weapon therefore synergises poorly with its actual purpose, and the only ameliorating factor is that you're likely to be keeping at least one other unit within 12" to get the benefit of its pain token distributing ability.
Spirit probe: Really not sure what this is intended to achieve, with only two attacks at such an average WS, it's perfectly possible that you could spend rounds of combat without achieving anything to use this upgrade with. Doesn't synergise at all well.
Spirit Vortex: It's a comparatively expensive upgrade, and brings the Chronos to the level of the Talos points wise, but it's the only option that synergises at all well with the unit's main purpose. It has a much greater range than the syphon, and means that you can stay out of assault range of most things whilst using it, and it should hit a lot more models than the syphon too. As an added bonus, if your opponent does get too close, because this is taken in addition to the syphon, you get the possibility of sharing out two pain tokens in that turn, not just the one.
Conclusion: The Cronos is a support unit that is intended to enhance your other units resilience faster than would otherwise be the case, and doesn't rely on wiping units out to gain those pain tokens. As such, in purpose it synergises well with a coordinated assault. The drawbacks however are that it's comparatively slow, meaning staying close enough to make use of its abilities is difficult. Added to that the fact that only the most expensive upgrade option makes the unit work, and its synergy could really only be described as average at best.
Razorwing and Voidraven
I'm dealing with these two together as they're very similar in both purpose and upgrades. Obviously as flyers they have no close combat potential. All of their upgrades address their long range damage options, with the vehicle upgrades reducing the damage that can come their way. All of these options synergise well with the units therefore.