3B plays closer to the batter, the balls get hit harder there, and you have a longer throw, plus you have to handle bunts. All of that means you have to make a lot of difficult plays. SS gets a lot of easy, routine grounders. Right handers trying to pull an outside pitch and such. I've played every infield position except 1B and including catcher. My order of difficulty goes like this: CA, 3B, SS, 2B.