I got a 15 gallon stainless with lid for under $100 off CL. I would hold out for stainless. 15 is great for 5 gallons, never boils over. 20 might get a little annoying because of size, but I wouldn't say it's too big. Plus it allows you to do a 10 gallon batch if you ever decide to split with a friend or something. Unless it's really wide, then your evaporation rate might be really high.