Stainless will be more durable than aluminum, but it will be more expensive.

One of the most popular, large pots these days is the Vasconia 32 quart.
It happens to be the perfect size to build a Mini WSM....Google it.
It would also be great for cooking crab.

http://www.walmart.com/ip/Vasconia-32-Quart-Aluminum-Steamer/10756126
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