The 'aluminum vs. stainless steel' (SS) pot debate pops up frequently, and given that we tend to see lots of new homebrewers enter the hobby shortly after Christmas, perhaps it is timely to post an FAQ on the subject.
Q: Is an aluminum pot OK for a boiling kettle in homebrewing? My LHBS only recommens using stainless steel.
A: Both aluminum and SS pots are excellent in homebrewing, and each has its own advantages and disadvantages, so it is purely a personal preference. Here are some considerations:
Aluminum Pots:
Pros:
- considerably less expensive than SS
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much better at conducting heat than SS, which means faster boils, faster cooling, and less chance of scorching
- not as heavy to lift as SS
Cons:
- oxidizes easily, meaning that oxygen-based cleaners (e.g., Oxyclean, One-step) cannot be used (Note: caustic or other similar clean-in-place solutions can definitely not be used, which is why the brewing industry generally does not use aluminum.)
- passive oxide layer must be built up before brewing (**see note below) with a new aluminum kettle, although it is very easy to maintain
Stainless Steel Pots:
Pros:
- can be cleaned by oxygenated/CIP cleaners without damaging the pot
- passive oxide layer that protects the pot is not as easy to remove as aluminum
- they are really shiny and look cool!
Cons:
- expensive
- not nearly as good at conducting heat as aluminum
Myths About Aluminum Pots:
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Aluminum pots will cause Alzheimer's disease. FALSE. This myth was debunked years ago by the medical research community, and the US National Institutes of Health and Health Canada have long since ruled out a connection between Alzheimers disease and aluminum cookware. If you dont believe me, see the following:
http://www.alzheimers.org.uk/site/scripts/documents_info.php?documentID=99
http://alz.org/alzheimers_disease_myths_about_alzheimers.asp
http://www.ehso.com/ehshome/alzheimers.htm
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Boiling your wort in an aluminum pot will cause off-flavours in your beer. FALSE. Simply boiling a batch of wort will not remove enough metal from your aluminum pot to get into your beer and cause metallic off flavours, particularly if you build up a passive oxide layer inside the pot first. For new pots, this is easily achieved by either boiling the pot full of water for 30 mins to one hour, or by putting it in your oven for 10 mins at 350 F.
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Aluminum pots have very thin walls, and are not suitable for a boil kettle, particularly if you want to install a ball valve.
FALSE. Thin- and thick-walled pots are made from both aluminum and stainless steel. The material they are made from is much less relevant that the thickness of the pot.
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Aluminum pots will react with very acidic materials, and wort is acidic.
NOT REALLY. Wort isnt acidic enough to cause a problem with an aluminum pot. In fact, both SS and aluminum are quite resistant to acidic materials, and you need to be concerned more about highly alkaline (i.e. basic or high pH) materials with your pots.
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Aluminum pots are simply not as durable as SS pots, so why bother, plus they will scratch easily and harbor bacteria.
PERHAPS, BUT... Both aluminum and SS are durable enough for homebrewing if you are willing to invest just a small amount of care for your equipment. You simply arent going to wear out an aluminum pot in your brewing lifetime, so this is a moot argument. Furthermore, scratches arent really a concern with a kettle since the heat of the boil is going to sanitize it anyways.
The Bottom Line:
You cant go wrong with a quality stainless steel pot, and they are a tried-and-true solution for lots of homebrewers. Yet, aluminum is a viable alternative that is much less expensive than SS. In fact, you can generally purchase a larger and heavier aluminum pot compared to the equivalently priced SS pot. In homebrewing, I guarantee you will really appreciate having a larger pot that is heavy and conducts heat well, speeding our boiling and cooling times and reducing scorching. In my mind, this far outweighs the cosmetic appeal and somewhat higher durability of a SS pot.
I have probably missed a few important points, but would be happy to ammend this post to keep it thorough and accurate.
The flow you get from just a 1/2" ball valve will make the reason for having one very clear the first time you use it. 
