Sorry to bring the subject back to starter trends, but my trend for favorite starters apparently has gone by "Grass, Fire, Water". Note that this only applies when asked generally which is my favorite starter of each generation and doesn't actually reflect which starter I pick for the game proper, I'm the kind of person who prioritizes team composition (no type repeats) over favorites for the in-game. Starters do get the comparison-advantage first (basically I see if there's another Pokemon of my favorite final evolution's type that I favor more, if there isn't, I'll pick that starter. If there is and there's a better fit in another starter, I'll go with the other one instead). I may have least favorites but I don't particularly make choices against them because of that (unless it's for online battles and they're just that bad competitively).
I'm not surprised why the original question went off-track - people like to state the reasons for their favorites and guess what, I'm not bothering to resist the urge of mine to do so as well, so here they are. I generally decide my favorites by their final evolution rather than the basics.
1) Venusaur - I was young back then I just followed the guide (which said Bulbasaur makes life easier). I don't deny there's nostalgia, but it helped I also liked supporting Venusaur as the underdog against the more-popular Charizard and Blastoise back then (well no statistics, but the general consensus felt like that back then and probably still marginally now), even if I have to admit if asked purely from a non-Pokemon general point Venusaur did indeed have least interesting design visually (but favorites don't care).
2) Typhlosion - I didn't like how overly-happy Meganium was compared to all other 5 existing starters then and Feraligatr always felt awkwardly designed in both sprite and art, even if I liked its concept. Meanwhile while Typhlosion wasn't outright vocally disliked (to be fair communication then wasn't great either), it did get comparisons to Charizard in particular and I felt it was an underdog because Gen 2 was pitted against Gen 1 even back then rather than against its own generation.
3) Swampert - I was admittedly out of the game when Ruby & Sapphire was in (and only returned then because of Leafgreen honestly), my entire bias for Swampert was mainly because a Cousin had Ruby back then I was just entirely influenced by his decisions back then that when deja vu happened in Gen 6, I went for Omega Ruby and Swampert. I do feel Blaziken was a rehash of Charizard when it came to hype (because people stopped comparing generations as much as Gen 2 suffered from) and Sceptile was just passable (and it was a Reptile fighting against Venusaur so my own personal bias comparions kicked in).
4) Torterra - This was the only generation I completely skipped out on. I just liked its design to be reminiscent of Venusaur (ironic considering Sceptile's case, but I guess it was simply because of different times). Empoleon gave me the awkward design feeling I got from Feraligatr and while some people didn't like Infernape for the typing-repeat, the sheer lack of fire-types in the region lessened that to the point I didn't really hear that dislike.
5) Emboar - The generation I "returned". OH BOY did the typing-repeat backlash hit hard on this one making Emboar the obvious underdog. It didn't help I was largely absent from the two generations prior exactly so I didn't have that typing-annoyance, but even that generation felt like a reboot of Gen 1, except the Grass & Fire starters switched places. I did pity Oshawott for a while, but eventually the entire line just felt neutral to me, somewhat like Blastoise. Note from this point I already recognized the trends in my favorites, so from Gen 6 on I'm not even sure whether I'm choosing favorites to keep the trend going on or not.
6) Greninja - I said deja vu for Gen 6 when I commented on Gen 3 because I skipped out on X/Y (I just didn't like how bland the story was compared to the entirely of Gen 5). I'm admittedly pretty neutral to all of them, but Greninja purely got the pick for its Hidden Ability which while I felt was "okay" for Kecleon, but great for a starter... I might have been just trying to continue the trend (considering Greninja might be the "most popular" of the three instead of the underdog in Gen 6 due to exposure), but the whole Generation felt so bland that I actually looked at the competitive side of things for this generation.
7) Decidueye - I don't have the competitive data yet and while I don't dislike Incineroar and Primarina for the common reasons people do (it would be refreshing for a non bipedal fire-starter though and the gender-aligned thing has been going around for generations already), purely from the visual design perspective, Decidueye does indeed hold the coolest design for me. While I did compare weaknesses when deciding for in-game purposes, it doesn't actually really affect my favorites (Tyranitar and Volcarona being some my favorites), so Decidueye retained its typings, the design would have still won me over (of course, it changed types and that's a bonus for post-game usage)... the only reason it's not being picked in-game is because I wanted to use Mimikyu more and well, they clash.
My favorites for Pokemon have always been weird - I do like Incineroar's typing and I like Lycanroc/Mightyena (canine Pokemon), so by all logic I should have liked Houndoom... yet I'm neutral to it, mainly because my brain can't seem to process personality for Houndoom as well as it can for the 3 Pokemon I mentioned and as a result it just lost character to me. I even felt its design was "generic" as a result (funny considering Mightyena should have been even moreso).