I wasn't commenting on the balance of the vehicles or the entertainment level of the associated gametypes. I find that the way UT3 vehicles control is WAY better than in 2k4, but that's obviously quite subjective. I also like the dynamic in Warfare more than in Onslaught, but again, subjective.
I'm sorry, I don't mean to offend anyone, but the majority of people who play Onslaught completely suck at the game. Note that I'm not saying people who play Warfare are any better. But, frankly, when you are dealing with a bunch of average players, it doesn't matter if they are in vehicles or not, and it doesn't matter if other average players are in vehicles are not.
Me and a few other people used to go on Onslaught servers and basically stomp them without even touching the vehicles. The player to vehicle balance is so bad that just having a small amount of aim and the right weapons means that very few people are going to kill you with a vehicle.
I haven't played UT online for at least a year I think, but I don't have any perceptible difference between the two games (except for the higher system requirements and all the stuff derived from that)... but this subject is again highly subjective.