I've used a lot of poly tanks where I can. They're impact resistant, don't rust and can be repaired by a couple methods (none of which are stellar but do work).
Down side is, in cases where the tank is easily visible a poly tank in an old car looks sorta funny. All of my old trucks have gone to poly tanks just for easy of use/no worry about rust.
I have never used an MTS brand, but just bought a 33 gallon big Bronco tank for a project I'm working on. Was 300 bucks with the tank, new sender, straps and isolators shipped.
Stainless is nice and doesn't look as out of place in older stuff, but they're pricey!