Purrloin/Liepard may be Unova's Meowth/Persian but I believe that they are more similar to Poochyena/Mightyena.
Both families are Mono-Dark Types available early in the game and are used by the villain team. Both are fairly useless until they evolve and at that point become fairly useful. At later points in the game they dramatically fall in usefulness as they are largely outclasses.
Which has the better design?
Which is more useful?
Which would win in a battle?
I'm going with Mightyena for all answers. Even if it loses usefulness, I keep it around simply beause having a great big black Hyena/Wolf thing at your side is quite awesome.