From MMOs to MOBAs, Spacetime Studios has you pretty much covered at this point. At least now that Call of Champions is officially available worldwide.
Call of Champions is meant to offer a somewhat distilled, 3-on-3 MOBA that's been tweaked specifically to cater to mobile users. This means shorter matches (~5 minutes or so) and fewer time-consuming mechanics that are normally found in the genre - such as minions or shops. Instead, players can find (and even share) special power-ups, and there's this "Orb of Death" thing that works kind of like tug-of-war but with orbs and tower destruction.
What's more, you can also hop in to Spectator Mode to watch other players and maybe pick up a few gameplay tips. There's even a feature that replaced dropped/booted/otherwise suddenly gone players with AI, so even if someone on your team has to take a call (or leaves due to frustration) you won't be down a champion.
You can download Call of Champions right now, for free.