I only have the 20gal kettle. It's a couple years old so they may have upgraded their construction. It just doesn't feel as sturdy as the Ss insulated mash tun and fermenters that I have. Again, just my opinion.
I don't think you can go wrong with either. I have three Ss fermenters so I may be a bit biased but comparing overall quality (I have a spike kettle) I like the construction of the Ss better.