I would go with stainless steel. I bought a brand new 15 gallon SS kettle with lid off of ebay for $95.00 delivered to my door and I absolutely love it. I am sure you can get a 10 or 12 gallon close to what you are looking at in SS.
This might be the beer talking....but I really love beer!
Aluminum can be fussy; you need to boil water in it to develop an oxidized protective layer, then be careful not to take that layer off by scrubbing, etc - too much work IMO. Get stainless steel and it'll last forever