I´v played HoN and LoL too.
But you can´t really compare those two with Demigod. Demigod offers you a much more deeper character development. The basic idea is the same. Go with your team and destroy their citadel. But Demigod offers you other gamemodes, too (not those game modes like "random heroes" etc.). Sure, compared to HoN you might think that Demigod suffers more demigods. I don´t know how it´s in the current build, but in the past I allways skilled my demigod a bit different. In HoN/LoL it´s allways the same. You got 4 skills, every skill maxed out. In Demigod it´s a bit more deeper. YOu have to watch the enemy, what´s he doing? Maybe I´ll take this skill instead of this etc.
One thing we can compare easily are the graphics. The maps and demigods in Demigod are just
The graphics and UI in LoL are just ->
In my opinion the graphics in HoN are ok (compared to the WC3 DotA). Compared to Demigod, they´re not as stunning as we got it here, but I still like them.
An other point I came across: The amount of players:
In Demigod we maybe have an amount of x players. In HoN we have 7*x players. Some people are adding "And it´s in closed beta!" Well, it´s not really "closed". Everyone who´s in the beta is getting about 5-9 new invites per 2 weeks or something like that. And the biggest point: You don´t have to pay yet in order to play HoN. I´m sure, there won´t be such a high player amount when HoN gets released.
Don´t know what´s the situation in LoL is. But it´s free2play and will remain as free2play.
In short:
Demigod is for people who like some new gameplay beside DotA.
HoN is for people who wanted a DotA2.0
LoL is for people who wanted to have eye cancer.