So my choices and the reasons why I chose them are kinda interesting.
I have played every generation of Pokemon since the original games, and before Black and White I had always chosen the grass starter. While many of the water and fire starters were cool too, this was my tradition and I loved them all. Now, Black and White were the first games where I was actually online to see the community's reactions and opinions on all things Pokemon. It was exciting, seeing so many others loving this franchise as much as I did. Then, the starters were originally revealed. At first I really liked the grass starter. I remember a lot of people liking Snivy (Smugleaf at the time as we had no official names). I also remember seeing quite a bit of love for Tepig (Since this was before the reveal of its fighting evolutions). However, the amount of hate that I remember seeing both for Oshawott and those who were willing to show their love for it was staggering to me.
Now, I've become very accustom to the various sides of the Pokemon community over the years and also know that these types of actions are done by a minority within the fandom so now I'm not bothered by it too much. But back then when I was new to it all though, I felt infuriated. It didn't help that most that were showing this hatred were also the ones praising Snivy as the perfect starter when we still knew so little about them. I grew to resent the little grass snake and grew to love the little otter. Then I remember seeing Dewott and Samurott and that's when I genuinely fell in love with this line. I hate to admit it, but I felt.....would validated be the right word? To see a Pokemon that was being bashed as horrible become such a cool samurai Pokemon felt so satisfying to me. It became (and still is to this day) my favorite water starter of all time and was an absolute powerhouse on my first playthrough of Pokemon White.
Then Black 2 and White 2 came out. At this point my dislike for the Snivy line (Being my least favorite starter line at the time) was still going strong. However, the figurative punching bag had been replaced with the Tepig line which was now considered the worse gen 5 starter line and even the worse starter line of all time by a few very loud members of the fandom. So just like with the Oshawott line, I gravitated towards the Tepig line and picked it for my first Black 2 playthrough. And I had an absolute blast using it. I love this flaming boar so much.
Over the years my hatred for the Snivy line has gone away, having come to realize that hating a Pokemon because of the hatred and toxicity of some people wasn't really fair. Plus I have also grown a huge love of snakes too. So after beating Sun and Moon, I booted up Pokemon White and used a Snivy for the first time. And while it could never overtake my love of Oshawott or Tepig, I loved using it and was very happy I did.
So tldr;
Oshawott for Pokemon White
Tepig for Pokemon Black 2
Snivy is my least favorite out of the three but is still a really cool pokemon.