I'm not by any means "good", but here're my two (four?) cents:
1. Based on watching people better than myself play, I can say that in general, the tablet is more popular at higher ranks.
2. The mouse is a hell-of-a-lot easier to learn to play with because the mouse is the peripheral of choice for most people.
3. I would expect that, as with other games in which players ask about preferable controllers, it doesn't really matter in the end, it just boils down to what you're better with. There was a guy at EVO USFIV, who you may or may not have heard about, who used a PS controller in Top 8. PS as in the first model.
4. If you have super-shaky hands, then screw the idea of a tablet altogether, unless you can train the shakiness out of your hands. Shaky hands are definitely better suited to a mouse and keyboard, with which you have a mounted surface to rest your (insert joint here) on.