What's your "Main 6" Attackers

1 Dragonite with Dragon Breath
2 Snorlax with Lick
3 Wigglytuff with Pound
4 Arcanine with Bite
5 Blastiose with Water Gun
6 Charizard with Wing Attack

Dragonite, DB/DP;
Exeggutor, ZH/SB;
Exeggutor, ZH/P;
Gyarados, B/HP;
Arcanine, FF/FB;
Vaporeon, WG/AT.

1. Exeggutor (Zen, Solar Beam) - 2 waters
2. Arcanine (Fire Fang, Fire blast) - 2 grasses
3. Vaporeon (Hydropump) - 1 Fire & 1 Snorlax
4. Golem (Mud Slap, Stone Edge) - 1 Snorlax
5. Wigglytuff (Pound, Hyperbeam) - 1 Lapras
6. Lapras(Ice Shard, Blizzard) - 1 Psychic & 1 Dragonite

Will use my own first, then what I think would be optimal...

Mine:
Exeggutor for the grasses (since they're all also poison so they're weak to him and he resists).
Vileplume for the Waters (assuming my Exeggutor can't keep going)
Vaporeon for the fire and Snorlax
Lapras for Dragonite and Exeggutor if he's the Psychic
Poliwrath for the second Snorlax and good damage on the Lapras
6th pokemon really depends on the CP of each of these and which Psychic it was - may want another Vaporeon, a (weaker) Snorlax, a Slowbro, a Victreebell, or may bring in a Nido against Snorlax and swap Vaporeon over to fighting a Psychic.

Optimal:
Exeggutor with ZH/Psychic
Exeggutor with ZH/Solar Beam
Vaporeon
Arcanine
Dragonite with DB
Lapras with FB/IB

The two Exeggutor will easily wipe the Waters and Grass/Poisons. Vaporeon for the Fire and damage on Snorlax. Try to save an Exeggutor to unload a Solar Beam on Lapras right as she spawns, then finish her with Arcanine - who will then go on to damage another Snorlax or beat the Psychic.
Dragonite deals with the two Snorlax or one Snorlax and a Psychic (basically Arcanine beats Psychic if it's not Slowbro, Dragonite otherwise).
Lapras for the Dragonite and to finish off any Snorlax health that may remain.

Jolteon
Raichu
Magneton
Porygon (with discharge)
Electabuzz
Electrode

I have what people would consider 'better' Pokemon, but that's my core team.

1. snorlax w/ lick and earthquake
2. exeuggutor w/ zen headbutt and solar beam
3. arcanine w/ fire fang and flamethrower
4. vaporeon w/ water gun and hydro pump
5. exeuggutor w/ zen headbutt and psychic
6. gyarados w/ bite dragon pulse

Venusaur
Wiggly×2(love these things)
Tentacruel
Lapras
Rhydon

Too bad gyms aren't as diverse as that sample though.

2 Dragonites with DB/DC plus Arcanite/Slowbro for Lapras. It will be more than enough.

1. Dragonite (Dragon Breath & Dragon Claw)
2. Dragonite (Dragon Breath & Dragon Pulse)
3. Lapras (Frost Breath & Blizzard)
4. Arcanine (Fire Fang & Fire Blast)
5. Exeggutor (Zen Headbutt & Solar Beam)
6. Vaporeon (Water Gun & Hydro Pump)

To be honest, the 2 Dragonites alone would almost take care of the gym. I do have a Snorlax too, but I don't like using it for attacking (I guess I would if the gym was high level enough).

1. Vaporeon with Water Gun / Hydro Pump
2. Arcanine with Fire Fang / Flamethrower
3. Vaporeon with Water Gun / Aqua Tail
4. Flareon with Ember / Fire Blast
5. Slowpoke with Water Gun / Psychic
6. Snorlax with Zen Headbutt / Hyper Beam

1. Arcanine: Fire Fang/Fireblast
2. Exeggutor: Zen/Solar Beam
3. Vaporeon: Water Gun/Hydro Pump
4. Gyarados: Bite/Dragon Pulse (I like Gyarados typing vs water and reliable dps from Dragon Pulse. Bite isn't too bad against Slowbros/Exegg and Gyarados doesn't suffer vs grass moves)
5. Snorlax: Lick/Hyper Beam (great vs exegg, awful vs other snorlax)
6. Wigglytuff: Pound/Play Rough cause STAB Pound is awesome and Wigglytuff is great vs just about anything

Exeggutor, ZH/SB ( Beany )
Vaporeon, WG/HP (Early )
Flareon, EB/FB ( Jet )
Vileplume RL/SB ( Petey )
Lapras FB/BL ( Soggy )
Pidgeot SW/H ( Ace )

My Kids named them for me..LOL

4x vaporeon is enough

Venusaur: (VineWhip/Petal Blizz)for the scum Vapo's

Slowbro: (Watergun/Psych (or ice beam depends on gym Dragons) also matches well vs other Psychs

Omastar: (mud/hydropump) can mow through 2+ fires and has resistance to normal moves..so a solid snoralax optionTry it

Pidgetto: (Fly/Fly)..should be rated wayyyyyy higher..plus matchups vs any grass, can take phsychs, and about anything else..(plus my Charizards both missed on Wing Attack ;)

1 Charizard or Arcanine with big big fire power of course

Wigglytuff: (pound/playrough) matches against about anything..and my favorite dodger with those moves..dragon moves extra ineffective..etc.