Let's see...
Kanto: Persian (<3!), Meowth, Blastoise, Charizard, Pikachu, Nidoqueen, Nidoking, Ninetales, Rapidash, Arcanine, Scyther, Lapras, Articuno, Mew, Starmie...
Johto: Espeon (<3!) Totodile line, Cyndaquil line, Noctowl, Ariados, Ampharos, Murkrow, Girafarig, Sneasel, Houndoom, Stantler, Lugia, Tyranitar, Raikou, Suicune...
Hoenn: Absol (<3!), Treecko line, Breloom, Skitty, Delcatty, Grumpig, Minun, Flygon, Bagon, Salamence, Spheal, Sealeo, Latias, Latios, Kyogre, Wurmple (leave me alone, it has the cute factor!), Crawdaunt....
Sinnoh: Glameow (<3! IT IS A SQUEAK TOY), Purugly (<3!), Turtwig line, Shinx line, Buizel, Pachirisu, Shellos (all), Gastrodon (all), Honchkrow, Stunky, Skuntank, Gible line, Croagunk, Toxicroak, Weavile, Rampardos (Pachycephalosaurs are cool), Gliscor, Lucario, Froslass, Dialga, Palkia, Yanmega, Shieldon, Bastiodon, Glaceon...
... Yeah. I have a ton of favorites. Overall though, Kanto is still my favorite gen and region, and well... Hoenn is my least favorite region.
Least favorites.
Kanto: There aren't any here that I actually hate. Probably because I'm just so used to seeing this gen...
Johto: CHIKORITA ugh. And Meganium. I'm all for dinosaur-like Pokemon, but... no. I'm neutral on Bayleef. It has this... attitude-like... thing about it that I like. Mareep, Flaaffy, Sunflora, Smoochum, Magby. Magby should not have anything that remotely looks like dreads. :( OMG CELEBI. It is a celery fairy. :(
Hoenn: Illumise, Volbeat, Nosepass, Castform (do not ask), Huntail, Gorebyss, Deoxys, Meditite, Lotad line, Seedot line, Slaking, all 3 Regis.
Sinnoh: Probopass, Mime Jr., Kricketot, Chimchar, Tangrowth, Happiny, Magmortar, Regigigas, Uxie, Mesprit, Azelf, Bidoof, Bibarel...
I may have more to put on here, but for now it's good enough. :3