I'm sure we all aim to rotate at the correct rate, as per the AFM. Personally, given the natural spread of results with manual manoeuvres, I think it's better to err on the slower side than the faster one. Reasons in no particular order:
a) Less chance of a tailstrike.
b) It's better to be above V2 than below it, in case of power loss.
c) You can always convert excess speed to height, the other way round doesn't work so well near the ground, especially when you're slow.
d) A rapid rotation at a slower speed generates more drag than normal so leaves you worse off in total energy terms.
e) If the aircraft is certified to clear all obstacles OEI from V1, with everything running you will be well clear - no need to snatch it into the air.
f) If you rapidly rotate to a high pitch attitude then lose an engine, it can require some quick reactions and deft handling to recover the situation.
g) It gives the person sitting next to you the willies...