Compared to past starters (and even the Kalos ones), the Unova ones are among my least faves. The only one I really like is Snivy due to it and its evos.' designs, typing, HA, shiny color palettes and movepool. I also found Serperior to be the best of the bunch competitively speaking, with access to Contrary + Leaf Storm, Leech Seed for health sapping, and Dragon Pulse to deal with Dragons.
Tepig I might've liked more if its evos. weren't Fire/Fighting and had better designs. It's a cute pig, but making its evos. part Fighting felt like a bad move, and Pignite's design isn't that good. iirc in Blaze Black and its variants Emboar is Fire/Ground, so if that could apply to it in the actual games, then i'd like it more. (Would also like Pignite to have a better design, but since I usually fully evolve my starters it doesn't really matter.) As for Oshawott, I like its and Samurott's designs, but that's about it. I'd like to add another typing to them, though I really dunno what would work. Maybe Steel, but then it'd nearly be Gen. IV all over again.
If these guys got Mega Evos., I can see Serperior being Grass/Dragon just like Sceptile, but I can't imagine how the other two would turn out.