From my point of view, a larger uke is slightly easier to play under certain circumstances, and a smaller uke is under others. I struggle to play a D as my sausage fingers don't all fit into the space required, but it's definitely more difficult on my soprano than on my tenor. I find barre chords, particularly Bb, easier on the tenor as well, as the string tension is slightly higher on the shorter scales making it harder to barre effectively. But something that spreads across several frets and strings (Dm7 for example) a bit easier on the soprano as everything is a little closer together.
As someone with fairly big hands (I'm 6 feet tall and while I have big hands, I don't have particularly long fingers), I personally find my tenor easiest to play, but this is in large part because it's a little more forgiving of my technique shortcomings.