1. A tie between bulbasaur and charmander. Bulbasaur has always resonated with me as a pokémon, and I love that it's a dual type from the get go. In Kanto, it's incredibly useful in the early-game, growing to be an absolute monster, and in Kalos, its bulk makes most battles a breeze. Charmander's line is objectively awesome-looking, and while it's tough to work with in early Kanto, after the second gym in Kalos, it tears through every other opponent. My charizard in X was the MVP of my team.
2. Probably totodile because it was the one I first picked in HGSS, though I love all the Johto starters. In Johto, the middle evolutions shine: croconaw is a good balance of adorable and fierce; quilava is, imo, better designed than typhlosion; and bayleef has the best middle design out of all three starters.
3. Treecko, but I've been developing a soft spot for mudkip. I wasn't really interested in Hoenn when I first played RSE, but in ORAS, my sceptile ripped through anything I put it up against, and its mega evolution design is pretty cool imo. I've also begun to appreciate mega swampert lately, and mudkip is adorable.
4. Chimchar, hands down, but I love all three. Piplup reminds me of ice cream and turtwig is one of the cutest pokémon out there imo, but chimchar's line has everything going for it. It's cute, but it evolves into something objectively cool-looking, has an excellent physical-special balance, is fast, is one of the few available fire types in DP before Platinum fixed that mistake... it's an all-round great 'mon.
5. Oshawott, but only for sentimental reasons. The samurott I raised in my hard mode White 2 solo nuzlocke single-handedly carried me through the entire game without fainting, and I only really decided to attempt a sololocke because my oshawott caught pokérus before the first gym — my only ever sighting of it. I'd not had a favourite Unova starter until that point, since I liked them all equally, but after that, oshawott climbed to number one.
6. Froakie. I love delphox's design, and I think chespin is super cute, but I hate braixen with a burning passion and quilladin is... mediocre in design imo. Froakie is the only one of the three that has an evolution line I like at each stage, and I think it's a great 'mon if you ignore the fact that water shuriken was a physical move in XY.
7. A tie between litten and popplio. Litten's evolution line is awesome and popplio's is beautiful. I don't really have much more to say; I just really love the designs.