I don't know about the other factions, but I think the Vanu guns feel horrible. At least the starting ones do, though I've since gotten a shotgun (Thanatos, I think). That one does feel OK, but still not great. I'll admit I am pretty bad with the shooting in this game anyway, not being used to having to aim down sights to be effective.
I went with Vanu because that's where my friends were. That's pretty much it. I feel like the faction is decent as a whole. I play on Jaeger and our map control is usually pretty good despite typically having the lowest population. NC never seems to factor in, while TR is on average doing the best (they also have the largest population, though). I don't think it's bad guns, vehicles, or anything that makes NC a nonfactor. They just (on Jaeger, at least) seem to not band together the way Vanu and TR will to make a massive push. And that's really what "wins" Planetside: Pure Zerg rushing. Just check out your continental populations. They're likely to be wildly skewed towards one faction.