The game I play most is Starcraft 2.

It's really hard to get "good" (I've played on and off for 2-3 years and still don't feel competent!) but the matchmaking is good enough that you win about 50% of games.

I like that it's 1v1, so when you win or lose, it's usually completely your own doing.

I also like that you pay once and are on a level playing field with everyone else. All of the in-game purchases are purely cosmetic. I played Hearthstone for quite a while but eventually totaled up the amount I spent on it and promptly quit!