Unova for my vote. Pointless #1 reason - Roxie's band!!
Although I wanted to desperately wanted to choose Kanto just because my favorite Pokemon (Persian) is native to that region it wasn't my main reason for choosing. I was forced between Sinnoh and Unova as my main area for voting. Just finished rewatching every episode from Sinnoh and love the layout of the region (I have not played the games based on Sinnoh yet).
How come Unova as my vote? it really reminds me of real life. A few large cities (Nimbasa City and Castelia City) to wonder around and explore, I also love the large areas to explore (I just arrived at the Elite 4 in Black2), I feel like I'm only half way through the game (still lots to explore). I can battle other trainers more than once (without having to find the vs seeker in FireRe/LeafGreen), the complex of the gyms (I got lost in three gyms before finding the leader) and my pointless #1 reason for Unova - Roxie's Gym!! at least the music, I could stay in the gym for 2 hours and never get bored.