240v just for shear convienance if you get the 110v you have to get all the transformer box too
Just make sure its variable speed and its quite slow on the slowest, the problem was with mine we got yesturday, even on the slowest setting, it was still quite quick, but have like 0 torque so it just slowed right down when you put it on the panel.
If you wanted to get the best you can get, Go for the Porter Cable, Ull have to get it from some company, i think screwfix sell them and plenty of places in amercia, and ull need the 110v transformer the cable with set you back around 120quid then the transformer is around 40quid.