Prestige

Against Snorlax, Wigglytuff!
Against Dragonite, Cloyster/Dewgong!
Against Vaporeon, Tangela!
Against Rhydon, Vaporeon!
Against Exeggutor, Parasect!
Against Gyarados, Jolteon!

Snorlax - Pidgeot
Dragonite - Tentacruel
Vape - Parasect
Rhydon - Starmie and Golduck
Eggy - Pidgeot
Gyarados - Raichu

I feel like vapes cost too much in potions, dont really like using them for training.

I have one twin account and I attack the gym until one level will not go away (-1000-3000 points, 1-3 battles). Then I take my primary account and prestige gym for 500-1000 points (1-2 battles). Damn very cold winter in my region! And spoofers.
(and sorry for my poor english)

Vs Rhydon = any water type
Vs Lapras = Wigglytuff, Magneton, Primeape
Vs Snorlax = Wigglytuff
Vs Dragonite = Dewgong,Magneton(with lots of dodging)
Vs Exeggutor =Pidgeot, Parasect(Bug Bite,X-Scissor only), Seaking(with Megahorn)
Vs Vaporeon = any grass type
Gyarados = any Electric type

I look for 1 or 2 lowest defenders on the gym to find out if I can make a good matchup where my attacker has less CP than the defender. This will result to 500+ prestige on defeating that defender.
I will not fight against all of the defender, because that will result to (individual) fights which will not give 500+ prestige but still require lots of healing potions.