I use both, Mainly because I bought 10 new carbon bearings for $5 once, So for .50 cents each, and on the shelf, they work fine. I also seem to pull the engine a couple times a year so replacing a carbon is no big deal.
However I do run a roller bearing on one of my Sprites and the other has a 5 speed with a roller bearing.
If I were to buy one because I didn't have it on the shelf, I would go for the roller bearing.