First of all, I want my ambivalence on the pokemon franchise to be VERY clear. I'm not a huge fan of the franchise and I haven't played any of the games since Crystal. If you must know my favorite pokemon overall is Heracross. That being said, when Sun and Moon came out and the buzz started hitting I noticed something strange, everyone seems to think the Grass starter is the coolest of the 3 "for once" and is pulling people away from the fire type, which is stereotypically thought of as the one people pick most. That being said I decided to take a good hard look at the fully evolved forms of all 3 starters from each generation and decide which one I think looks coolest (PURELY my sense of aesthetics, my judgement has nothing to do with their abilities or usefulness of their attacks.)
Generation 1: canon turtle, dinosaur with tree on back, and fire dragon. I think Venasaur probably has the most unique design of the 3, but honestly even if it is just a basic western style dragon in red Charizard just plain looks coolest, probably why its one of the most famous pokemon and got to be a character by himself in Smash Bros 4.
Generation 2: Apatosaurus with flower collar, blue Leatherhead from TMNT, and giant honey badger with fire collar. This is a hard one becuase all 3 of them look so...unspectacular...the grass one looks like a less cool dinosaur, the fire one doesn't gain the ability to fly, and the water one barely looks like anything...except for a character from another franchise. When I had gold I used Typhlosion and Feraligatr in Crystal, and had a botched playthrough with Meganium (battery failure deleted my save file halfway through, I cried for hours.) Ugh this sucks, these starters sucked and were so unimaginative, there is no winner here next generation!
Generation 3: Festive Geico Gecko, incredibly weird looking salamander, and superchicken. I HATED generation 3's pokemon designs overall, but these starters looked good at least in their 3rd forms (though I will NEVER get over how much Combusken looks like a penis.) Still, despite such a sketchy second form I have to say Blaziken wins this generation for me, though Treecko and grovyle look really cool to me and easily beat out the other 2 at those evolutionary stages, this was a real come from behind win for the fire type.
Generation 4: Turtle Island, literal emperor penguin, and the monkey king (though it really looks female with the golden brazier thing going on...) This is a hard one, because Infernape and Empoleon both look so awesome. Sorry Torterra, but you look more like an ordinary turtle than Squirtle, you barely qualify as a "monster" to my sensibilities. This is an even more subjective opinion than most of my choices so far, but I'm going to once gain go with the fire type and say Infernape is my favorite because it looks like it can do kung-fu.
Generation 5: Snake queen, unicorn seal, and Ganon. This one is almost too easy, the Zelda fan in me can't resist the awesomeness of fire boar. Hmm...gee it seems that the fire starter DOES win all the time...
Generation 6: Ninja frog, wizard fox, and robot...uh...sloth? Okay...all three of these guys are awesome for different reasons, it's like the ANTI-Generation 2, I almost can't pick a winner because all 3 of them look so cool. I THINK for the fandom this is where the water starter broke the fire streak since Greninja is apparently so popular it got to be a character in Smash Bros 4 like Charizard. I wonder how they decided that? Since all 3 of these guys have a humanoid form hypothetically any of them could have been stuck to the frame of a character in a fighting game, was there some kind of poll or was it just Sakurai's personal favorite? Unable to choose for myself I'm going to go with the apparent majority and say Greninja was the coolest of this generation, so for the first time the fire starter got unseated in the popularity contest.
Generation 7: Pro-wrestler cat, Robin Hood Owl (or should I say "Owl-Hood?") and mermaid seal. So we arrive at the current generation, and something of a theme is how there is usually only one fully evolved starter that isn't a biped, except for 5 (which had only 1 biped) and 6 (which had all 3 be bipeds.) Still, I think all 3 of these are pretty cool looking, even mermaid seal that kind of has a mystical air about it, probably because the character art depicts it in a Little Mermaid pose. You know what? I won't choose a winner for this generation either. They obviously put real thought into making all 3 of them look good in different ways and I find that too admirable to denigrate by picking one over the other 2. What do you think?