Actually if you not too obsessed with the rank given, you wont have to rage a lot. Just enjoy, and you are not increasing the mmr as if your future career depend on it. For me, MMR is a lot better than normal game cos out of 10, you manage to get at least 5 match that is high standard or to your standard, which is what MMR for.

But if you serious about increasing ur rank, there is a few hero which more all rounded like Mirana, WR, Pugna, Invoker. But it wont ensure victory, it still depend on ur team performance. Also when MMR, do not random, do no fail pick! If you random and fail too badly, u most likely to get report. Also just remember no flaming, no blaming, else u get report as well lol.

Still lately I havent meet any bad player, or player that fail as badly as normal match, so i guess its still not that bad.