I suppose ones who need it. The main benefit to mega evolution is the huge pile of stat bonuses that gets heaped on top of you, so ideally you want to be giving them to a Pokémon who a) mainly suffers from a low base stat total, and b) is an unlikely candidate to ever receive a conventional evolution. So, for instance, Klinklang is a poor choice because Klinklang’s problem is having a minuscule skill set, not lacking the raw power to use that skill set, while Dunsparce is a poor choice because, as a one-stage Pokémon with lower base stats than Sneasel, Gligar and Tangela, there is still plenty of room to just evolve him. There are better answers than mega evolution to their problems. So which ones do I think would be the best choices…? Hmm… Scanning down the list of Pokémon in the same general area as Beedrill (the Pokémon with the lowest base stat total to be given a mega evolution so far)… well, I think Ledian, with her interesting and diverse offence/support movepool and total lack of the kind of power necessary to back it up, is a natural choice; Bibarel has a unique type combination and interesting abilities, but they just don’t compensate for the fact that Bibarel sucks all around; and… let’s say Delcatty; Delcatty has a ridiculous movepool that she’s incapable of using, and we have a built-in excuse to rework Normalise into something actually decent while we’re there. I’m also going to break all of my rules and offer Plusle and Minun, because there you could do something interesting with their teamwork theme by allowing them both to mega evolve off of a single mega stone if you use them together in a double battle (I mean, let’s be honest, they’ll probably still suck but at least it’s interesting).