he can be played anywhere, really.
I've done him top, mid, adc and jungle all with shitty games and hard carries. But I suppose top and mid would be his best. Although mid may be more of a counterpick. If the laner is melee, he will have a better time.
Urgot lanes best against AD champions due to itemization but I'd say don't worry too much about what he's "best" at because people are convinced he's shit no matter what, so if you work hard enough you can make him work anywhere.
Sometimes I will play him adc just so I can have an excuse to not build any defense what so ever, full ad/arpen Urgot is scary AF xD
The reason bot lane is seen as his worst role is because he is not an auto attacker. You should never buy infinity edge or attack speed on him, all his damage comes from Q with the occasional auto here and there