I'm just going to get this out of the way early so I won't have to later on and have people ask questions.
I actually do play HoN a little and I love it. Personally, I play LoL more but that's only because my friends play it since HoN costs money. That's one thing about LoL, you don't have to pay a cent. Sort of.
If you don't buy anything with money in League of Legends then it's basically impossible for you to get every champion. At the same time though there's free weeks and you will rarely ever need every champion in the game.
HoN is fairly cheap for the replay value (Especially since i got it when it was only $10, hell yeah). It's a lot more fast paced and games seem to go a little quicker.
They both have their ups and downs and are both great games. They feel a lot different but skill does somewhat transfer over between the two. It's like comparing apples and oranges, it's hard to do. Even though oranges are obviously superior.