best for what? choose your parameters, ie 16's for comfort, 17's for looks ... you need to consider the width of the rim, the offset, and also the tyres you fit.
I run 15's and 16's for the commute (winter, summer) and 17's for track. Should probably run 16's for the track as well, but found some 17x7 OZ SuperTurismo's in ET40 and ... (well, you know how it is ...)
For fast road use and also for looks. I've got a set of 17" webspokes on run flats (I know run flats are bollocks but its what the car came on) but I'm looking for some new alloys that would be suitable for fast roads and also look the bomb.