What I will do here is outline the various pros and cons with a short summary statement. With the amount of Pokemon you've listed I am loathe to do anything too long as it will be (boring) far too long.
I will start with Competitive analyses followed by an in-game one.
Chesnaught -
Cons: Low speed, poor typing for this Gen, outclassed.
Pros: Decent ability, good Attack and Defense, good signature move, strong STAB moves, acceptable movepool to work from.
Cons: Low speed, poor typing vs four out of eight gyms, Super effective typing vs one gym.
Pros: Good typing to face down two of the E4.
Summary: Chesnaught is a decent Pokemon with capabilities this Gen, unfortunately his typing is already taken by another Pokemon who is easily more usable than he is, that Pokemon is Breloom. I'm sorry to say that while this guy does have his pros, he just can't do as well as Breloom can, especially with such a poor speed.
Diggersby -
Cons: Poor stats, with highest being an average 85 HP, poor typing, not many roles to fill, looks ugly (this has no affect on the analyses but it's worth mentioning).
Pros: Huge Power (HA), capable of sweeping.
Cons: Poor typing vs 3 gyms, poor stats make it less effective late game unless over-leveled.
Pros: Good vs 2 of the E4, good against 2 gyms.
Summary: While this guy has almost everything, he's missing out on the stats. With below 100 stats in everything he's just not going to be able to pull off quite the same roles as many other Pokemon can. Competitively his one buff is Huge Power which will definitely aid in giving him a chance in the lower tiers.
Goodra -
Cons: Poor Defense, abilities aren't as helpful as they could be (especially with weather nerf).
Pros: Special Defense stat is through the roof, decent attacking stats, good HP, good movepool to work from.
Cons: Can only get it later in the game, meaning that it faces off with two gyms that hurt it badly.
Pros: Resists two of the E4 and has great survivability with it's HP and SDef stats.
Summary: Goodra is a great Bulky Attacker, with potential as a Toxic + Rest staller, with a killer SDef stat a good SAtk stat and a relatively decent HP stat, it can tank hits and deal them out extreme tankyness.
Clawitzer -
Cons: Bad Speed, bad Defenses.
Pros: Moves work particularly well with ability, strong Special Attack.
Cons: Weak to two gyms, not caught until later in the game.
Pros: Resists three of four E4 and has a move that hits three of four of them.
Summary: I'm not for using this guy competitively, mainly due to poor speed. Even with max speed and a Choice Scarf he falls short of the acceptable mark. However in-game I would say this fella is great to use, his Speed can be patched up using EV training and he's great against the E4.
Gogoat -
Cons: Poor Defense and Speed stat, weak to many common move types, Abilities could be better, limited roles.
Pros: Dat sexy HP stat, ginormous horns, and good recovery moves.
Cons: Grass, nuff said.
Pros: Really I'm getting tired of doing this so I'd like to say one thing, I used him to sweep the Kalos Champion.
Summary: His Defenses are poor and his limited move pool doesn't help. His speed means he can't effectively sweep, although can fill the role of Tank, however there are sadly others who can do that better. In-Game he's great, I seriously love Gogoat, my one and only favorite grass type.
Noivern -
Cons: Other than Speed, stats are fairly lacking for the higher tiers, For example it's highest non-speed stat is Special Attack which is 97, 4x weakness to Ice
Pros: Infiltrator, some great moves to work with.
Cons: Not achievable until later in the game and weak to two of the gyms.
Pros: Resists two of the E4 and has the move to kill the Steel E4.
Summary: Noivern is a threat to be considered despite its ears, Infiltrator makes it great at destroying many of the SubPokes seen competitively. In-game, it has the stats and frankly it's kinda cool having a Bat Dragon on your team.
Pyroar -
Cons: Bad Defenses, terribly unhelpful abilities, 106 Speed base means that it will lose out to Terrakion and Keldeo.
Pros: Good Speed and Special Attack, strong STABs.
Cons: Huh.
Pros: Strong against several gyms, is available very early on, does well against Steel E4, while managing to hold it's own against the Fire E4.
Summary: While I'm not huge on using Pyroar in competitive battling, due to being outmatched in his potential roles, he's great using in-game. Only weak to two gyms and capable of holding his own against three of the four E4. He also looks really cool.
Talonflame
Cons: 4x weak to the most common entry hazard.
Pros: Gale Wings and access to Sword Dance ensure maximum sweeping capabilities.
Cons: Dies fairly quickly due to poor HP and Defenses.
Pros: Strong against several of the gym leaders and able to hold it's own against 3 of the E4. Can learn and effectively use HM Fly.
Summary: Talonflame is good to use in-game and incredibly dangerous to use competitively. It can be hard to use competitively though if you lose your spinner and if Rocks is up, however once you get a SDance up you basically say gg and spam Brave Bird everywhere.
Vivillon -
Cons: Less than satisfactory stats, 4x weak to the most common entry hazard.
Pros: Compound Eyes and access to Hurricane, can effectively sweep with Quiver Dance.
Cons: Weak to several gyms, and weak to one E4 and no move to hit another E4 (steel)
Pros: IT'S SO CUTE!! But seriously, Compund Eyes and hurricane, with potential Quiver Dance sweeping in-game.
Summary: I used Vivillon and I liked it. It has roughly the same capabilities that Venomoth has, but weaker to entry hazards. While Vivillon does have the ability and a nice move, it's outclassed by other Quiver Dance sweepers such as Volcarona.
Hawlucha
Cons: Basically a toned down version of Talonflame with higher speed and lower attack.
Pros: Each of those abilities is beautiful, Limber, Unburden, and even mold Breaker.
Cons: Doesn't evolve.
Pros: Dat Speed tho... Also has access to SDance meaning that it can sweep in-game.
Summary: As I mentioned it's really just a toned down version of Talonflame, capble of running a great Dual STAB Acrobatics and Hi Jump Kick paired with SDance and Roost carrying Flying Gem with Unburden, this monster can sweep as well as any Scarfer, but with the power of someone with a Choice Band.
Sylveon -
Cons: Florges wannabe much? Bad Defense leaves it open to physical attacks, while a slow speed leaves it vulnerable to a lot of those slow, yet powerful threats, like Mamoswine.
Pros: Fairy typing, with weaknesses easily covered, Strong Special Defense, Special Attack, and HP stats. Good Support movepool.
Cons: Ummmmmm, Geee, let me think. That sums it up I guess.
Pros: Same as above, easy to evolve using Pokeaime. Good against the Dragon E4.
Summary: I haven't used it because I prefer Florges, but it's still a good Pokemon who can fill the role of team support really well. Also got the kind of Special Attack the'll work in-game.
I ran out of space....
