In the long run think Priefert's powder coat paint will hold up better, especially if outside in a higher rainfall area. Whatever brand you get be sure to get the adjustable width chute.
I have no experience with either of those brands. Stur-D pretty much owns the market "here".
Not what you asked, but if I were in the market for a tub/alley/chute setup I would likely get Stur-D simply because I'm quite familiar with and have a lot of experience using the product.
Likewise, if you like one brand better than the other and are comfortable using it, get the product that "fits" you.
Neighbor who bought my place owns a portable Stur-D tub and alley. He uses his old Pearson chute on front of it.
In the long run think Priefert's powder coat paint will hold up better, especially if outside in a higher rainfall area. Whatever brand you get be sure to get the adjustable width chute.