Good luck mate! Playing both and deciding on your own is the best option. You won't get good answers from a league subreddit on why you should play Dota instead of LoL anyways.
Just to clarify some misconceptions LoL players seem to have:
They often seem to believe that snowballing (getting ahead early into the game and just walking over your opponent from there) is a huge problem in Dota compared to LoL. That's absolutely not the case, quite on the contrary.
The difference they don't seem to get is that in Dota you lose a lot of gold whenever you die, and the stronger you are compared to your opponent, the more he gains from killing you. So being ahead by lets say 20%(gold, experience) and dying once will even it out again.
LoL will be the better game for the first 50 hours at least, since as I said before, you lose gold when you die, and like others said, Dota is a lot more punishing overall. You have a turn rate, which means when you're facing towards your opponent, turning around to run away will take you something like 0.5 seconds. Disables in Dota are generally a lot longer than in League, which means being in a bad position for only a split second can mean you're dead again.
Which game suites you more really depends on how much time you want to invest into it.
Both communities are enormous, so the size doesn't really matter. Both communities are shit, so I don't think that matters either way.
Dota is superior in terms of features, I think there's no denying that. There's voice chat and pausing a game in case your cat catches on fire. There's a good replay system, you can see fight recaps, you can jump into a replay if you have enough players to fill the slots and replay a game from a certain point, to try whether you could have won had you just not made that one critical error, things like that. The free to play model is also superior, since there's nothing in the store that actually gets you ahead of people who don't pay, and there's no new skins for heroes, so you have an easier time differentiating between heroes (it's easier to tell a hero is the same as before if the only visual difference is a new hat, instead of a completely new look)
Overall I believe Dota is the clearly superior game non-gameplay-wise. LoL has made it a lot easier, which is of course a great thing. It's like hearthstone is a great card game, but old MTG players will probably despise it for being too simplistic. I'm an old school Dota player, so the game being a little more complicated in it's mechanics doesn't bother me at all, that's why it's my game of choice.
If you're completely new to the genre though, just play both as you already said you would, and probably choose League, since you'll probably be less frustrated playing that game :)