Jim Carrey no doubt!
The mask , Ace Ventura , dumb and dumber , trueman show , batman! Sandler aint got shit on carrey.
Edit: Also Jim Carey plays many roles , I have seen him be serious or sometimes just a goon. Sandler plays the same charecter in different films , nothing wrong with that but if it comes to who is the best actor I would say Jim has more range too .