Pasted from This vs. That thread:
Brew Pots: Stainless Steel Vs. Aluminum Vs Enamel
(Note: Much of the Aluminum/SS information is taken straight from FlyGuy's post here. He did it first, and it was a very well written post. This information is transcribed here only for the sake of having one central database for as much Pro Vs. Con information as possible.)
Enamel:
Pros:
Many kitchens already have an enamel stock pot of sufficient size to do partial boil extract batches
If you have access to a second-hand store, enamel pots are generally the least expensive on this list
Clean in place (CIP) type cleaners, such as PBW, Oxiclean, and One-Step can be used
Poor heat distribution, meaning that once you get your steeping water to the appropriate temperature, it's easy to keep it there
Cons:
Eventually, even with proper care, the enamel coating will chip, rendering them unusable for brewing
Fairly heavy, making shipping more expensive
Generally not available in sizes larger than ~3 gallons, making full boils impossible for a standard 5 gallon batch
Poor heat distribution, making for slow heating and cooling
Cannot be drilled for ball valve installation. This isn't a huge deal since you wouldn't be using a small enamel stock pot for an all grain batch, unless you're making smaller ~2.5 gallon batches
Aluminum:
Pros:
Generally the cheapest kettle available in 5+ gallon size
Very light weight, making for cheap shipping, and easier transportation and pouring
Excellent heat distribution, resulting in rapid heating and cooling
Easily drilled for installation of a ball valve. This can come in handy when/if you decide to move to All Grain brewing
A new aluminum kettle will last for the length of your brewing lifetime with proper care
Cons:
Passive oxide layer must be created and maintained. This is done easily enough by filling the kettle with water and boiling for ~30 minutes. You'll know it's there when the inside of your kettle has a brown discoloration
Although an aluminum pot will likely last for as long as you need to use it, it probably won't last forever. If you inherited your great-grandparents aluminum pot, leave that for spaghetti
CIP cleaners cannot be used without damaging your pot. With aluminum, you'll need to use old fashioned manual labor
Stainless Steel
Pros:
Shiny! Who doesn't like the gleam of stainless steal equipment?
With proper care, you'll be able to pass on your SS brew pot on to your great great grandchildren. They just plain last forever
Can be cleaned with CIP cleaners
Passive oxide layer is much easier to maintain than with aluminum
Easily drilled for installation of a ball valve. This can come in handy when/if you decide to move to All Grain brewing
Better heat distribution than enamel
Cons:
The most expensive kettle on this list by far
Much heavier than aluminum. More expensive to ship, and more difficult to transport and pour
Much less heat distribution than aluminum. Slower boils, and harder to chill quickly
