Kanto's nice and all, but the starters aren't all that interesting. Especially the Squirtle line. I *like* Charmeleon, Charizard, Bulbasaur, and Ivysaur, but the first two aren't all that creative(generic lizard/dragon with flame on its tail) and the last two are a tad more creative(badass frog with a plant on its back) but nothing special.
Johto maintains a fairly uniform level of design goodness throughout, although nothing other than the Totodile line and Quilava stand out to me a great deal.
Houen...come on. I'm sure most of you know my opinion on the Treecko line, the Torchic line's good(Torchic being decent, Combusken being great, and Blaziken being fugly), and the Mudkip line's cute for two stages and cool in an ugly way for the last stage.
Shinou...I like the first and last stages of the Naetle line(the first stage mostly due to the anime >>) although I could do without the bore of the second stage; the Hikozaru line's nice and all, but Hikozaru's boring(flaming butt aside), Moukazaru's Charmeleon only a monkey(basically a generic monkey with a flame on its tail, which would be cool if they hadn't DONE IT BEFORE only with a different animal), and Goukazaru looks ugly as sin in sprite form, but it's actually pretty cool in the Sugimori art(why it took the line that long to reach a form that's at all appealing to me, I'll never figure out. I mean, how hard is it to dissapoint with two fire monkey Pokemon?); and the Pocchama line's just awesome. They're cute, decently cool, and fecking awesome. In that order.
Really, I'm torn between Johto and Houen. Mostly because they're consistant with how good the starters and their evos are. I'm sure my opinions of the Shinou starters will mellow out over time and they'll join their previous gen counterparts in that catagory, but for now...