I like the way of earning champions in LoL. It reduces my natural ADD and makes me focus on the ones I have. Of course, I've been playing for awhile now, so I have... damn near all of them.
I prefer LoL over DOTA2 because I like the minimalist approach. Not in terms of champions (there's a fuck ton of those) but in terms of mechanics. DOTA2 has a lot of mechanics that feel extraneous to me. Denying farm, denying tower kills, losing gold when you die, all of these things were once in LoL and were removed because of their impact to gameplay. DOTA2 is a much more complex game in terms of mechanics, but you can find infinite complexity in a smaller system by refining the mechanics you do have.
Overall I suppose it's all just taste. I played both, I liked LoL a whole lot more.