FXO = Slow start, slow on the straights, slow out of turns, slow in turns, but Good under braking. Lovable, but now crap. Aparently it understeers, but i can't say i've noticed :P
RB4 = Wierd powerband, lots of grip, lots of grunt. Eats XRT's and FXO's for breakfast whatever the surface. Pick if you want to win.
XRT = Nice engine and power, RWD gives some... hairy moments - harder to drive, but rewarding, nice cars, nice power, gets owned by the RB4, but owns the FXO. Has lots of understeer.
I love the way you say the XRT is easy, but i have to "pray to god i don't crash"
FXO is probably easiest, RB4 is fastest - if you want to win the RB4 rocks, its easy and quick, the XRT is more rewarding to drive, but i just LOVE the FXO