Recently switching to Ableton from Cubase I can tell you that with the way I use midi, the timing isn't overly flash at all in Live.
I can bypass the computer with a good old fashioned midi router in my setup, so testing between Ableton's midi by ear is easy. In ableton, even just when playing, there is a very slight delay that you can feel (almost like the difference with 5ms of vs 15 or 20ms of audio latency). If I play from my controller through the old fashioned midi router box I have, I can not feel any lag or latency. Cubase wasn't like this at all.
I don't stick up for Access much at all, but in this case I'd say its live.
EDIT: I should say that this is only with using my hardware synths and samplers etc. Not easy to bypass the computer when using software synths etc.
