Agh DX! When I started Black 2 I picked Tepig solely for the reason that I didn't have one in either White 2 or Black... and I needed one to complete my Pokedex in my White 2 save file (once I get 3ds for trading critters between my games, that is). At first I actually considered having Emboar on my team, mainly because its design is still somewhat bearable and leaving the starter pokemon to rot in PC simply isn't my style; the only time I've done it in the past was with Pokemon Yellow... But then I went to Bulbapedia and checked Emboar's stats: abysmal defense and special defense combined with below average speed. Add the fact that many Pokemon learn Earthquake and you have one cumbersome and somewhat ugly-looking fighter on your hands.
Thus I replaced my Pignite with a Growlithe that eventually evolved into Arcanine . But I have to say that it's usually the grass type starters that get the least inspiring or flattering design. The exceptions to these are Swampert and Emboar; I consider them to be the weakest link of their respective generations.
Swampert, weakest in regards to design? Hm, I guess I could agree. It's really nothing spectacular. My fave list of Hoenn starters finals are Blaziken, Swampert and lastly Sceptile. I just don't like Sceptile's looks. He's ugly. Grovyle was cools as shiz but then they ruined it with Sceptile... Balls on its back, really?
When it comes to movepool and coverage and overall performance in R/S/E, Swampert is definitely the winner. There is no grass gym in Hoenn and that leaves Swampert with either having super effective moves or neutral moves against gym leaders (including the Whitney of Hoenn, Wattson) and in general there are very few threats for Swampy in Hoenn. So if you're looking to do a nuzlocke challenge in R/S/E, pick Mudkip for an easy run.
I'm thinking Chespin evolution line is based of Armadillos but this clearly based on the design of Chespin's Stage 2, Hariboogu is similar in design as an armadillo and it can use Roll-out and Mud-shot so mostly like the final stage will be either Grass/Ground (I hope not) or Grass/Rock