2 eggs, 2 vapes, 1 jolteon is the standard I can use to take a gym in my area.
The 6th will be one of these 3 or maybe a Rhydon if I find Snorlax, or Lapras if there are Dragonite.
I may use a Dragonite, or Alakazam or some other generalist if I feel like mixing it up - but most of the time I can get away with the basic 3.
Of course, it depends on what is in the gyms in your area.