I'm going to post my favourite starter from each region, if that's okay. It'll be kinda hard to pick, though.....
Anyway, Kanto's an easy one -- Charmanader, without a doubt. I picked him as my started when I first played Pokemon Red Version years ago, and have loved him ever since. One of the main reasons is because I really like both of his evolved forms.
Johto is alot harder, but I'd have to go for Totodile. Again, he's the dude I picked when I first played Gold. I like Cyndaquil, but not very fond of his evolved forms. Yeah, so I have to go with Totodile.
I'm not a fan of the Heonn starters, but I'd more than likely pick Treeko, mainly because Ash had an awesome one in the anime.
Sinnoh was pretty much the same as Heonn, not a good selection of starters. I'd go with Chimchar, though. His evolutions are pretty awesome, too.