From those three, I prefer Dota 2 miles aways. Most importantly, because all heroes are available. After that, the gameplay in Dota 2 is way more entertaining. Denying creeps, stacking neutrals, reliable gold, Roshan, stuff like that.
LoL I played it mostly before I got an invitation for Dota 2 beta. I don't like their business model too much of locking the heroes behind paywalls. The rune system and trees weren't interesting for me neither. The gameplay is too simplified for my tastes, don't like that most items are (or were, dunno too much of current LoL) just passive and, if memory serves me well, champions are forced to be on the same lane always. Of course, I could be wrong but when I used Riven, I was forced to go top, regardless of side. Again, I could (and most likely) be wrong.
HotS, I only played some matches. Not my tastes. Even more simplified than LoL, and the same business model as LoL. So yeah, I skipped it.