I'm not a tits man and they often spoil things, you feel under an obligation to do something even though you aren't interested, I've had the occasional good tit wank but that is down to the dirty look on the girls face and where the cannon is pointing and would probably have been even better with a hand wank in the same position.
Huge boobs I find a total turn-off, its a shame because many girls with really nice personalities have huge tits (probably a confidence thing?).