Persian. Taken straight from smogon.com:
[quote]It has a little more Attack than Persian, but other than that, Purugly is totally outclassed by its feline counterpart.[/quote]
Also, besides being better in EVERY ASPECT other than Attack, Persian also looks just way more awesome. It can look cute, it can look mysterious, it can look mischeivous, and it even can look a bit evil. Purugly's just a cat that looks like it got thrown into a trash compacter. Remember the first season of Pokemon when Team Rocket wasn't just stupid comic relief? Giovanni had a Persian, and it looked BADASS. I don't remember Purugly playing even a somewhat important role in the show. Really, Persian has just always seemed better to me. Maybe it's because I think every 1st Gen Pokemon except for a few (Jynx and others) seem well designed and just awesome to me. I dunno.