15 gallon pot!!!!!!!!!!!!!! you won't regret it. 10 gallons and you might regret it. It gets tight doing a 6 gallon batch (which you will want to set as your standard if you don't already) in a 10 gallon pot.
Coming from the owner of a 10 gallon pot.
Up next: Kolsch, Alpha Squirrel, Tripel rebrew, Witbier
Currently Fermenting: Charlie Sheen (barleywine)
Kegged: Tiger Blood IPA, Irish Red, Strict Observance Tripel
Bottled: Dry Stout, Pliny the ..... Squirrel?, Cream Ale