Mando is a good choice. He gets a lot of hate but I really don't see why. I blame jealousy because there are a lot better artists, but he gets to hang out and be friends with the show cast and stuff cause he was first.
To be honest, I've only liked Tombstone when he first started, but then I noticed all his songs have the exact same drum sequence and its an abysmally simple one at that.
Though call me a hipster if you will, but I enjoy artists like
Cherax Destructor,
SoGreatandPowerful, and
Le Soldat Pony, just to name a few.
Of course you can't forget Black Gryph0n though. He's probably the most talented (don't fight me) composer/mixer/singer/musician in the brony fandom.