Eldar. All their weapons have different names, different stat lines, and different looks. If you've never really sat down with eldar, it can turn into confusion and complete fail on the tabletop, as you wonder what each unit can really do. Lets take a look at two of their vehicles, the wave serpent and the falcon. Not knowing the difference can really mess up your target priorities. Both are fast skimmers with a variety of upgrades. Lets look at their defenses first, because knowing which one to shoot with what is the first step to understanding these vehicles.
The Wave Serpent. This is a dedicated transport, and it comes standard with energy fields. Energy fields reduce all weaponry to str8, and all ranged attacks never roll more than 1d6 for armor penetration. This means that str 8 weapons like missile launchers and others like autocannons are an efficient weapon to shoot at these armor 12 vehicles. Also note that on assaulting, you get full strength, and dont have the problem that Holo-fields provide on the damage tables. However, these are skimmers, and probably moving very fast making them hard to hit in assault. (you need a 6 to hit most of the time if you can even reach them)
Now that you know how to efficiently shoot at these vehicles, the next step is to know whats in them. Seer councils, and firedragons might be your obvious first transport priorities. To break the wave serpent spam lists choose the right weapon for the right job. Then you can fall back on weapons that are less efficient.
While their weaponry can sport bright lances, pulse lasers, eldar missile launchers, I tend to ask what is on what. Remember that bright lances reduce all armor values above 12 to 12. Otherwise, I'm generally more concerned about whats in them, and what I have that can bring down that vehicle, rather than what they are equipped with. (that's the easy part of target prioritizing).
Last thing to remember. Eldar players tend to do a lot of tank shocking and ramming with these vehicles, as they are considered to be tanks. So expect tank shocking/ramming fast skimmers.