I can't see myself leaving LoL for Dota 2, unless they migrate more from the original dota formula. I played HoN for a while, and it is basically what Dota 2 sounds like to me: Dota with a better backend and nicer graphics. LoL made the formula a lot more fun, with champions seeming a lot more uniquely designed (I think the 'passive' system helps a lot with that) and a more wide-ranging system of itemization that gets away from the strength/agility/intelligence model. Especially as somebody who has a preference for casters, they scale infinitely better in LoL than they do in dota. Plus all the persistence features in LoL are a nice touch.
Finally, the LoL community can be a bit rough at times (though Tribunal has already seemed to help) but it is WAY WAY WAY better than HoN or Dota ever was. Every few games I end up adding folks to my friends list (even from the enemy team). That never happened in HoN or Dota, where 9/10 you will get yelled at by both your own team and the enemy team.
I'll probably check dota 2 out, they could do a lot of good with it. However, the original dota crowd basically hate change (even HoN was apparently too radical for some) so if valve wants to capture that market, they will have to change the game as little as possible. In which case, I almost see no reason to play it over HoN, if all you're looking for is Pretty Dota.