I'll write one up for Oshawott:

This guide is when this little guy is your partner.
Samurott @ Mystic Water

Trait: Torrent
Hasty Nature (+Spd, -Def) or Naive Nature (+Spd, -SDef) or a neutral nature (Bashful, Quiet, Hardy, Serious....)
This starter is a complete HM slave. 4 HMs on Pokemon? Let's go.
Samurott's mixed attacking stats make this set not too bad for ingame. Surf, Waterfall, and Dive are all HMs, gain STAB, and get a Mystic Water boost. Cut cuts down trees. I hope you knew that. This allows you to get better moves on your other 5 Pokemon.
Where to get the stuff for this moveset:
Mystic Water: Route 4, Castelia City
Cut: Virbank City
Surf: Route 6
Waterfall: Victory Road
Dive: Undella Town
Obtained: As a starter Pokemon
Arcanine @ Leftovers

Trait: Intimidate / Flash Fire
Jolly Nature (+Spd, -SAtk) If you can.
- Outrage
- Flare Blitz
- Thunder Fang / Wild Charge
- ExtremeSpeed / Strength
Arcanine is chosen over the popular Darmanitan for several reasons. Darumaka's Hustle may hinder its performance, when them random misses occur, Darumaka can easily get KOed by a Water Gun or something like that. The second reason is that Growlithe is found quite early in the game; in the Virbank Complex. Third and most important: it gets Outrage. Outrage is dead useful ingame, destroying almost everything that doesn't have a resist, and has nearly perfect coverage with its Fire move. It also helps against Drayden, as well as defeating Kyurem-B/W and N's Zekrom / Reshiram. Flare Blitz is its STAB move, and hurts. But the recoil sucks, so Leftovers help in remedying the solution. Thunder Fang, which is found using the Heart Scale to the Move rememberer, covers Water Pokemon. Wild Charge is an option if you want more power. ExtremeSpeed picks off weakened foes, or you can use it for Strength. Now, to the abilities. Intimidate is the superior choice, as it will allow you to take more physical moves with ease. Flash Fire can be used to soak up Fire moves.
Where to get the stuff for this moveset:
Leftovers: Castelia Sewers
Flare Blitz: Level 45 as a Growlithe
Outrage: Level 43 as a Growlithe
Thunder Fang: Move rememberer at PWT for 1 Heart Scale
Wild Charge: Victory Road
ExtremeSpeed: Move rememberer at PWT for 1 Heart Scale
Strength: Castelia Sewers
Obtained: Virbank Complex
Crobat @ Muscle Band / Shell Bell

Trait: Inner Focus
Naughty Nature (+Atk, -SDef) If you can.
- Fly
- Cross Poison
- Heat Wave / Dark Pulse
- Roost
The team's Flyer. Enough said. You can get a Zubat at the Castelia Sewers, which is pretty early, and it will screw Burgh over as a reward for being caught :3
Fly has decent power and STAB, and helps you travel around Unova easily. Cross Poison is obtained by Heart Scale and is better than Posion Fang for its power. Heat Wave nails any annoying Steel types, while Dark Pulse can be used to hit Psychic types. Roost heals off any damage you took.
Shell Bell: Driftveil City
Muscle Band: Battle Subway / PWT
Fly: Route 5
Cross Poison: Move rememberer at PWT for 1 Heart Scale
Heat Wave: Move Tutor in Humilau City for 10 Yellow Shards.
Roost: Move Tutor in Humilau City for 6 Yellow Shards.
Obtained: Castelia Sewers
Zoroark @ Life Orb

Trait: Illusion
Hasty Nature (+Spd, -Def)
- Foul Play
- Night Daze
- Flamethrower
- U-turn
This guy is so boss ingame.
This is a mixed set, as Zoroark has great stats in both spectrums.
Now, let me introduce you to the best move to this set: FOUL PLAY. This works EXTREMELY well against Drayden and Iris, who both have Dragons with high attack and access to Dragon Dance. It kills all the things. Night Daze is STAB, and works off Zoroark's good Special Attack. Flamethrower roasts Steel Pokemon. And Bug Pokemon. U-turn keeps momentum. While momentum isn't that important, you can switch Zoroark with your Crobat to provide x4 immunities.
Life Orb: Battle Subway / PWT
Foul Play: LV 29
Night Daze: LV 64
Flamethrower: Route 23
U-turn: Move rememberer at PWT for 1 Heart Scale
Obtained: Driftveil City
Upon request:
Genesect @ Expert Belt

Trait: Download
Hasty Nature (+Spd, -Def) or Naive Nature (+Spd, -SDef) or a neutral nature (Bashful, Quiet, Hardy, Serious....)
- X-Scissor
- Flamethrower
- Ice Beam
- Thunderbolt
The standard Genesect set, except with X-Scissor instead of U-turn. X-Scissor is your STAB, and the other 3 moves are coverage. Can't really explain much, but Expert Belt and the coverage this thing provides will rack up loads of damage.
It is advised to use Flash Fire on Arcanine to patch up this guy's Fire weakness.
Expert Belt: Driftveil City, Route 19
X-Scissor: LV 51
Flamethrower: Route 23
Ice Beam: Giant Chasm
Thunderbolt: Victory Road
Obtained: Event
Haxorus @ Muscle Band

Trait: Mold Breaker
Jolly Nature (+Spd, -SAtk) If possible.
- Dragon Dance
- Dragon Claw
- Earthquake
- Low Kick / Strength
Haxorus is the monster of the team. this guy is insanely powerful ingame. You can capture an Axew in Mistralton Cave.
Axew has axes, I mean, access to great moves. Dragon Claw and Dragon Dance are learned quite early on. Dragon Claw is your STAB. Earthquake nails Electric types and Levitators. Low Kick is your Fighting type coverage against Ice types, while Strength can be used over that if you didn't do so for Arcanine.
Muscle Band: PWT / Battle Subway
Dragon Dance: LV 32
Dragon Claw: LV 28
Earthquake: Route 15
Low Kick: Driftveil City for 8 Red Shards
Obtained: Mistralton Cave