Mudkip is rather well-known (I take it you know why, because that meme is everywhere...) so Swampert gets plenty of exposure because of that. I wouldn't call it one of the lesser-known starters.
That out of the way... let me try to put some real thought into this post. Apologies in advance if I ramble/this becomes a little too long. (Read: It'll be a lot too long.)
I feel that I'm still searching for the team I want to have, but I'm not entirely sure what I want to use as a whole. It'll take time, I'd say, and I don't know if I'll ever set on one concrete one that I'm entirely happy with... I hope I will, but I can't say for sure...
My starter for Reborn was Tepig. There were very few starters I hadn't used recently- the only ones being Snivy, Tepig and Turtwig (this was in Episode 10, so Gen VI wasn't in yet), off the top of my head. Three very different Pokemon. My love for Fire as a type + a bit of the horrors I'd been hearing about Florinia's Cradily finally cemented the decision.
A decision I can't say I've regretted, per-say. While not a stand-out among my team members, by any means, Spiggy (quick warning: my nicknames are dorky and will only get dorkier from here on out) pulled his weight well, and if it was dealing damage I wanted, then it was dealing damage he would do. The biggest thing I can remember him doing is being the one to take down Spectral Kiki's Medicham so many times, in my quest for a shiny Gastly. He has finally been rotated off of the team, and I'm still seeking another Fire-type that can fill the hole he's left behind... I'm working on getting a Chandelure as I type this, and we'll see how that works out.
The rest of my team has rotated on and around, but... I have a few things that have stuck over time, and one new addition that hasn't had a proper test run yet, but I've already started to form a bond with. Because I'm dorky and form bonds with my pixels yes. But I'll get to that.
First, we have Blair, my Skuntank. I spent an extremely long time in the Underground Railnet hunting for a Stunky, since Skuntank is my favourite Poison-type, and I was quite eager to have one when I'd heard it was in the early game. My efforts paid off in the long run, because he has helped me in several key situations. Namely, he was my MVP against Shade, taking down four of his Pokemon (three on his own, one with help, I believe) and he is also the only reason I beat Luna on the first try. I don't know if he'll stick around until the very end, but he'll be staying for now... he's actually the only thing besides Spiggy that's remained consistent this long, I've just realized. Huh.
Picking up Sir Vale, my Gardevoir, as a Ralts in the early game was an impromptu decision, I'll admit. Back when I was still naive to the ways of Reborn (I am not now, at least, not as naive) he was the one who claimed victory against Julia with a really terrible Double Team strategy- one that was almost entirely luck. He's participated in a lot of important battles (the most noteworthy being against Corey's Crobat [before Episode 11 again, so he wasn't Fairy-type then] and Radomus' own Gardevoir) and he was temporarily rotated out in favour of a faster Psychic-type in my Espeon, but I've opted to take him back as of late.
Bayou the Swampert was a switch-in for my Azumarill- I wanted something that could take hits just a slight bit better than he could. He's definitely proved that he can do that, and dish out a good chunk of damage as well. As he's a relatively late addition, he's not gotten much use- the most noteworthy bouts he's had are against Radomus' Metagross and Luna's Tyranitar. I'm quite fond of him now, though, so I don't really see myself switching him off the team.
And, though he's still an extremely new addition, I'm already quite attached to Cantus, my Meowstic. I'd wanted something for more of a "support" role, and I'd been tossing the idea of using my preferred Meowstic form- the male one- as a dual screener around. Lo and behold, I went through with it, and with the little use I've gotten out of him as things are now, he's filling his role well.This is also my first use of Meowstic, so I was a bit worried... but he's living up to and beyond my expectations, as it is now. I suppose I should wait to see how he fares in an actual serious battle to determine whether or not he's really what my team needs...
There are other things I've used that I won't be going into detail on... because this post would be a bit too long if I did, but for one reason or another, I've decided to swap them for something else. Currently my sixth slot is taken by Echoes, my Noivern, but I don't feel that I'll be keeping him for good...
I used Persian (Grimmjow), Azumarill (Ruri), and Simisage (Cleanse) earlier on, took on the trifecta of Roserade, Gengar and Espeon (Fern, Shade and Radomus- can you guess why they're a "trifecta"?) for a short time after Episode 10s end, and I've used Dusclops (Chateau), Marowak (Vigil), and Ninetales (Kurama) for specific Gyms, but not much else.
...I mean, I know you didn't ask for my entire team history, but... I feel the need to give credit where credit is due. I've used a bunch of Pokemon- people recommend rotation here, to combat the level cap, but I've never actually hit that, regardless of whether I rotated things or not. I just can't rotate forever... I need to be prepared for the Elite Four way down the line and have a proper team put together for that, plus I'd like to just have that one team and be able to say "Hey, I conquered the game with these guys, they're awesome" but that won't happen anytime soon.
...I think I got a little too emotional about this post. Going back to breeding Snubbull now. OTL