Vainglory

Hearthstone is also a good one if you're more into CCGs. Prime World Defenders has gotten me lately too, though that's just a single-player game.

For me the question is are there any games where you can trade time for money. Which is to say you can be just as good/powerful/equipped as any other player who spent $x by putting in y minutes of play time. And then what is the factor 'k' such that $1 = k? Basically what level does skill play in your cost of levelling.

it's a little older and more for tablets than phones, but Frozen Synapse is well regarded

That's the best way I've heard it worded. Makes it more obvious than "pay to win."