Oh, definitely Flygon. It totally deserves a Mega evo, and was
eleven going to get one in ORAS if not for creative/time
constraints. Although it's not my favorite pokemon, it was cheated
out of a mega evolution, which isn't particularly cool.
Definitely Flygon. It's one of my all-time favorite Dragon-types,
and I think it was a shame they overlooked the poor thing because
of design troubles. Dragonite as well, if only to chuckle at how
they could possibly name its Mega Stone.
As for personal favorites I'd love to see with Mega evolutions, I
elect Weavile, Gliscor, Luxray (who has a good chance if they
remake or re-release D/P/Pl), Excadrill, Bibarel (for the lulz),
Butterfree (to balance Beedrill), and Froslass (since we already
have Glalie).
Volcarona, Scolipede, and especially Leavanny are deserving
of Megas. Leavanny really needs the boost. More ideas are Mega
Flygon, Mega Tauros, Mega Miltank, and Mega Floatzel.
also, flygon. i was honestly pretty surprised when he didn't get an
evolution in oras, when i heard the team of artists couldn't think
of any ideas i was pretty disappointed.
here's some mega flygon designs i'd like to see in-game.