Banette, mostly because of the name but also, I like the idea of giving ghosts another evolution, especially if it's one that Ash has never seen before. Hope it appears in the anime but other than that, a great idea to revive that ghost!
Milotic should definitely get a mega evolution. It has great bulk and a competent special attack stat but suffers from an abysmally shallow movepool. I like the ideas that TyranitarTube (of YouTube fame) had about it's possible mega evolution.
Here is a link to the video: https://www.youtube.com/watch?v=IrVyRZHfyA8 (Milotic starts at 3:20)
some pokemons tend to have crappy mega evolutions.. such as pinsir, heracross etc. game freak should have shown more intrests in other legend pokemons. like ho-oh and lugia etc. anyways great job with mega alakazam and mewtwo they look really cool. any suggestion on which pokemons actually deserved mega evolutions?
Mega Pinsir is a beast!
If you're talking about rubbish megas you must mean Mega Aggron