Kanto -
Didn't care for many Kanto Pokemon, so this one was easier compared to the next tow regions. Dewgong wasn't my favorite for a long time; I would even say I overlooked her. For many years I was obsessed with Flareon, and the rest of my team were just randoms that I didn't particularly enjoy. Recently, I've taken quite the liking to Dewgong and used it as my water type in White 2.
Johto -
This was a bit tougher, as Johto is my second favorite region. Many Pokemon could have stolen this spot, but I went with what has always been close to the top of my list of favorite Pokemon. I have at least twenty Pokemon cards of Flaaffy, and since the second movie was released, I've always been in love with it. Ampharos, although still a great Pokemon that I've utilized many times, just didn't deliver on what I was hoping for. :[
Hoenn -
The most difficult decision came here, because Hoenn has grown to become my favorite region by far. Honorable mentions include Flygon, Gardevoir, Masquerain, Mawile, and Swampert, but Absol takes the cake. Its design is majestic, powerful, and beautiful. Again, its presence in one of the movies helped solidify this decision. Overall, a wonderful concept and one of the best Dark types in the game.
Sinnoh -
Sinnoh is my least favorite region, so not too time consuming to pick one. Azelf always intrigued me, after I had used it as my utility Pokemon in competitive battling for a while. Eventually, I began to use it in-game, and I personally wish it wasn't a legendary, because I would've caught one early in the games to use if it hadn't been. Still, takes the Sinnoh spot.
Unova -
The easiest decision of them all; Mienshao is my favorite Pokemon and so, obviously, it's my favorite from Unova. There's so many things I could say about its design or appearance, but its niche comes in battle. Usually, the Pokemon I like aren't necessarily strong, but Mienshao packs a serious punch, and crushed the Unova League almost by herself. A brief stint in OU tops of the résumé of an amazingly useful and gorgeous pokemon.
Kalos -
Not a huge pool to pick from, but Skrelp caught my eye the moment I saw it. Unlike Spritzee, its evolution didn't fail to meet my expectations. In fact, Dragalge exceeded them. Unique typing, sleek design, and a nice movepool make for quite the Pokemon. Only drawback is, just by looking at it, one would think Dragalge is at least moderately fast. Unfortunately, those who think so would be far from right. Dragalge is annoyingly slow, which greatly cripples his capabilities. Nontheless, he's one of my favorite Pokemon!