I voted for the Pidgey line, Sandshrew line, Mewtwo and Lugia.
For anyone who knows me, I reckon the Pidgey line would be kinda self-explanatory, seeing as it's my all time favourite Pokemon. I don't think that many actually know the story behind why that is, but that's probably because it's as simple as it gets. Pidgey was the first Pokemon I ever caught myself and trained to level 100 myself. Blue was the very first game I ever owned, and I shared it with my brother, so I honestly didn't really have that much autonomy within it, as I couldn't really get to train any Pokemon for myself without him nudging in on it all, though to be fair, I got a lot of Pokemon to level 100 that way :p But yeah, Pidgey was the first one I got, and I managed to convince him to not use it, and while it may have gone a lot of the game without use for that exact reason, and thus making it difficult to actually train it to level 100, since things like the VS. Seeker and stuff didn't exist back then. But it happened! And I honestly don't know why I prefer Pidgey over Pidgeot, but that has just always been the case. And that's why it'll always remain my favourite :p Doesn't look like it's doing too well in this though :(
Sandshrew is entirely because it's Alex' favourite Pokemon, and I feel obligated to vote for it :D
I voted for Mewtwo entirely because it's still one of my favourite legendaries to date, however as time has gone by, it's kinda lost its popularity. It used to be the Pokemon all the kids were talking about on the playground, and every battle it just came in LIKE A WRECKING BALL (sorry), and it was just completely outmatched. I think my main issue with it was that it was too easy to catch compared to how strong it was, so that kinda made it feel less special, but eh, everyone still loved it anyways :p But yeah, it's been nerfed quite a bit since its glory days, and it isn't even considered the most powerful Pokemon in the world anymore due to Arceus making an appearance, but I guess nothing lasts forever :(
Lugia's because of a story I've told idek how many times now, seeing as it keeps popping up in votes all around the forum, and especially in clubs, so not gonna tell it yet another time! :( Basically, some guy totally wrecked my brother's team in his Gold version, which I'd always considered really powerful, with one single Lugia. And at the time, I knew the Pokemon obviously existed, since it appeared both on the cartridge as well as in the title menu of my Silver version, but I had no idea where it was, seeing as the location in which you could find it wasn't nearly as obvious as what Ho-oh got. But I guess that was pretty much because of its tower burning down. Poor Lugia :( But yeah, after seeing what a creature of massive destruction it was, I went searching for it. And I searched for such a long time. Like seriously, I'd already looked in the Whirl Isles prior to the time I actually found it, but apparently I didn't look hard enough! But yeah, I eventually caught it, and it was amazing, and it became my favourite Pokemon of that generation, as well as my favourite legendary ever, and I always used it. Also note that English isn't my first language, and I was like 5-6 at the time, and all the English I knew at the time was yes and no, so even though it was stated within the game where Lugia was located, I always just skipped over the stuff 'cause I couldn't read it!
oops guess I told the story anyways. Anyways, those are the reasons for my picks :)