I played it almost exclusively up to level 30 (I joined LoL when Riven came out).
When Dom Elo was squashed for the last time though, I got really frustrated and switched over to SR to play ranked. Was fun at first because it was something new, but all the reasons people list here as problems with SR has dropped it down.
Now I mostly play ARAM. That ****'s fun and the random aspect of it helps keep it fresh. Part of me hopes it becomes a game mode for more even matches, other part doesn't because I do like how laid back it is.
I play Dom and SR on about an equal rate now, probably more Dom. If I play SR though it's as a jungle, as that is a lot more fun than laning. Still takes forever and all that good stuff but ganking lets fights happen and such, and huge impact on all lanes.