Hmm, not as pithy as I'd hoped...
Anyway. Personally, I like six Raptors - partially because that's what I've got, but it does make for a nice, affordable unit that's still got some punch. Two meltaguns (perfect for a unit that moves 12"), an AC with twin lightning claws, and an IoK to round it out. You've got your anti-tank punch, and two S8, AP1 shots going into combat, followed by twenty "regular" attacks and five from the AC on the charge. Never hit a tarpit if you can avoid it (and you usually can with jump packs) - gun for low-model, high-cost units. And all that for 210 points. Nothing better than highly mobile meltas for taking out a Land Raider. Just remember to avoid squads with more than twenty models, or the lethal combination of power weapons and high Initiative.
Four Colditz salads and a Hermann Goering.