You can't really say "college to pro" transition when most guys are drafted at 18 out of high school, Latin America, Major Junior hockey or foreign pro leagues. Of course a guy at 18 is going to take longer generally than a guy at 21-23 (like in the NFL) or even 19-23 (like in the NBA).

If you just looked at college guys, I think you'd find their transition to be sort of similar in those minor league oriented sports. Certainly it's true in hockey, you see a lot of guys come in as undrafted FAs from college and get in the game quickly or finish out a little more of their NCAA career and jump right in. Same thing in baseball, guys coming in at 22 from major programs are not going to spend as much time in the minors, maybe none.

What positions? I think catchers in baseball, defense in hockey, tackles in football (LT a little more so than RT I guess), quarterbacks obviously, centers in basketball and, probably the most demanding adjustment, would be a goalie in hockey.