That's hard to say. The XPVC seems to be the popular choice these days. I looked on SSScales website for his economy racks and they seem to be the best option in my opinion.

http://ssscales.com/archives/290

This design also looks good to me. It is kind of like a rat rack with freedom breeder style heat. Its something to consider.

http://www.baileyreptiles.com/cb70rack.html

There are a lot of options.