I won't go through wild Pokemon, but here's my analysis with the starters.
If you like more defensive and stall Pokemon, I would suggest Chespin. When it becomes fully evolved, its typing (Grass/Fighting) may appear weak to a lot of things, but its bulk makes up for it, with its very high defense. It also learns moves like Leech Seed and Spiky Shield that help to make it very hard to take down. In addition it's got high attack with some very powerful physical moves like Seed Bomb, Wood Hammer, Hammer Arm, and Earthquake.
Again though, this Pokemon is very defensive rather than offensive and should not be expected to quickly sweep things.
If you are looking for a very fast and versatile pokemon, though, I'd suggest Froakie. Greninja has almost equally high attack and special attack, with very impressive speed to boot. Though its defenses are pretty low, its job will simply be to come in and knock things out. Its moveset is pretty good too, naturally learning moves like Night Slash and Extrasensory, and learning a lot of great TMs for even more coverage like Acrobatics, Ice Beam, Rock Slide, Grass Knot, U-Turn, and more.
Overall a pretty fun Pokemon, you just have to be careful with letting it get hit. Also it's WAY more fun with its hidden ability, Protean. :C Still very fun though and probably my favorite of the starters I used. Don't feel bad if you decide to keep going with it haha.
The best of both worlds, though, would be Fennekin. Delphox has pretty reasonable stats all across the board, but with especially good Special Attack, Special Defense, and Speed. It learns a bunch of pretty sweet fire and psychic moves, but isn't as versatile with the rest of its moveset. Some worthy moves to mention that it can learn are Shadow Ball and Grass Knot. (yeah... not much. I put Light Screen on mine and that was helpful.)
Keep in mind that the fire/psychic typing is very nice offensively, but defensively, it has a lot of weaknesses. Still a very stable Pokemon overall and definitely not bad.
I hope this helps with your starter selection! Ultimately whatever you choose it'll be great. [:
Pretty much any Pokemon from the wild you choose to use will be fine as well. Some are definitely better than others, but the game is easy enough so that you can use even the less-than-strong Pokemon and they'll still probably be decent.
Some comments on a few pokemon that people mentioned -
Furfrou is awesome, I loved it so much when I used it haha. I taught mine U-Turn, Surf, Dark Pulse, and Return. It was a lot of fun for me. Not the best by any means, but I still loved him. I feel like he's underrated.
The fossils... I'm not so crazy about them. I used Aurorus my first playthrough because it's just so pretty and wonderful. However it's weak to so much, it kept continuously fainting, especially when I was first training it up. However after a while it got easier... with some caution and persistence I think it can be a great member on your team [:
Tyrantrum on the other hand was just simply outclasses by other dragons, like Haxorus or Goodra or Noivern.
In short, just use whatever you like. [: I wish you all the best with your game~
