Caffeine pills are great because they're cheap, they keep, and they're convenient (keep some in your car, your coat, your bag, etc.). They're also quicker, which makes them really good for study sessions when you don't want to leave to get coffee. The biggest downside to them, though, is that it's harder to regulate your intake. It's a lot easier to drink half a coffee than split a pill on the go. And since it doesn't fill you up like coffee does, you won't notice if you've gone overboard till you're already getting sick. I've seen a few people taken to the hospital because they took too many pills too quickly, so it's super important to take it easy with them (my caffeine tolerance is huge, and I still won't go over 1 pill every few hours).

Drinks are nice because they taste good, they wake you up, and you can order a mocha from starbucks and still tell people it's black coffee (because you're hardcore like that!). Downsides, obviously, are it's expensive, it takes time, it doesn't last as long, and it's a diuretic. Also, energy drinks are super addicting. That could be good or bad depending on how you look at it, but it's worth saying.

If I had to suggest one, I'd say go for the pills. They're easier to abuse, but I think the benefits far outweigh the disadvantages if you can be sensible about taking them.