I agree with most of the others, Aerodactyl is one of the best Flying and Rock-types in the game given it's fast and a solid strong physical attacker plus it's one of those Pokemon you don't have to wait until postgame to obtain its Mega Stone (Aerodactyl's Mega Stone is obtained in the fossil lab in Ambrette Town) and as Rauzo said, once you get to the Move Relearner in Dendemille Town (which is around after the 6th Gym) you can get some really good moves for it. You can revive Aerodactyl from an Old Amber, which are found through smashing rocks in Glittering Cave, although sometimes Onix and Dwebble may show up as well.
Espurr is pretty solid Psychic-type, and I used Meowstic in my playthrough which did its job pretty well I have to say. Although I think the female might be slightly better in-game given she gets some extra attacks and I don't usually do defensive play in-game that much. The two different gendered Meowstic both learn some different moves leveling up, so take some consideration into which one would suit better.
Both are useful on their own, it just depends which one suits your team better.