Pokemon Green. My first pokemon game despite being a bit late in the know-how.
I got hooked after battling a few battles, (and a few annoying moments between an Abra, Gary and some weirdo who wears shorts) and I felt the rush that it will be big. Plus the fact that I get a dinosaur-like friend rocks. Venusaur and Charizard were my favorites. =w=
I absolutely loved Emerald. It was my first Pokemon game, and I fell in love with it. I still take it out and play every once in a while, working on that pesky Battle Frontier. It very well could have been the best Pokemon game of all time.
My favorite is Emerald! It was so exciting with double battle & the battle frontier! They even had team Magma & Aqua both evil corporations! This game was a powered-up version of Sapphire & Ruby. I just hope they make a remake of it!
I've gotta say HGSS because they cover my favorite regions and because they brought back the ability to have a Pokemon follow you around. I hate, though, that they changed the casinos and I can't say I'm impressed with the Pokethlon.