Best counters

I wouldn't put dragonite in any of then, because he is not a counter of anything, he is just freaking strong against everyone except ice, and a COUNTER is something good against that one specifically.

I would put Rhydon on n1 counter to snorlax since he:
1 - resist most of snorlax attacks
2 - Do super efective damage with rock smash.

anyway, good list !

Lapras: Jolteon, Raichu, Machamp (KC/CC)

Exeggutor: I normally use Arcanine, Charizard or Parasect with BB/XS.

Vaporeon: Any mon with 2 grass / electric moves, I have used a part from the one you mention Tangela, Electabuzz, Raichu, Vileplume or Victreebel

I am tired of seeing the same mons that's why I normally use different ones to attack them even if the fight takes a bit longer.

Dragonite:

Dragonite without HB.

Cloyster without HP preferly Blizzard.

Lapras preferly Blizzard.

Dewgong for training.

Magneton with FC.

Jolteon if the defender Dragonite has SW.

I'd rather use Scyther w/ FC/XS against an Exeggutor instead of Jynx and Jynx is weak against Dragonite's Steel Wing, otherwise looks decent

Note: pinsir with RS and submission is not useless; I use them to counter snorlaxes.

Parasect w/ BB/XS for Exeggcutor and BB/SB for Vaporion are good if you have moderate dodging skills.

Pidgeot with Wing Atk and Hurricane is surprisingly good vs Snorlax. I have a 1300cp one I use for prestiging. If you had a top IV one max out with Wing Atk and Hurricane it would be pretty good I'm sure if I can beat them with a 1300cp one.

Plus if the Snorlax has Lick it isn't very effective. I was very sad when Pidgeots got nerfed last patch but they make for great prestigers vs Snorlax

Machamp against snorlax lapras and rhydon if u like him too..

I like to use Primeape w/ low kick & cross chop vs. Snorlax. I find that even with a large CP deficit Primeape can dominate snorlax pretty well, even without dodging absolutely everything, unless it has zen headbutt

Gyrados with HP is good against Snorlax and way better than a Alakazam.

These are what I normally use as my top 3 counters...

Snorlax :
Vaporeon with Aqua Tail or Hydro Pump
Gyarados with Hydro Pump
Wigglytuff with Pound/Play Rough or Hyper Beam (best for prestiging)

I somehow don't like to use Rhydon fast move as the animation seems too slow... just personal preference I guess.

Lapras :
Arcanine with Fire Fang/Fire Blast
Machamp with Karate Chop/Cross Chop
Omastar with Mud Shot/Rock Slide (Would prefer to have Omastar with Rock Throw but that is legacy now...)

Exeggutor:
Pinsir with Fury Cutter/X-Scissor
Charizard with Wing Attack/Flame Thrower or Fire Blast
Pidgeot with Wing Attack/Hurricane

Dragonite :
Lapras, Cloyster, Dewgong all with Frost Breath/Blizzard

Vaporeon:
Exeggutor with Zen Headbutt/Solar Beam
Tangela with Vine Whip/Solar Beam (best for prestiging, eat Vap. for breakfast!)
Venusaur with Vine Whip/Petal Blizzard (I have no luck getting Venusaur or Victreebel with Solar Beam)