I prefer the aluminum versions. They would seem to be much more durable than plastic and I've seen several older plastic ones that had deformed. Summit has some aluminum 4 & 5 gallon sizes that may be worth considering. I have an aluminum 10 gal. now but will eventually go to a 5 gal.
http://www.summitracing.com/parts/SUM-293205/
http://www.summitracing.com/parts/SUM-293204/