We have weathersheild casements, though for astetic reasons, have all wood cladding/stucco mould exteriors which means maintenance. We are very impressed with the quality of the seal/ locking mechanisms but i feel andersen makes a quality window as well. Imo, both are quality units, so you might want to factor in what would look better astetics wise for your build. I believe weathersheild offers more options concerning the r-values and types/thicknesses of panes, u.v ratings, etc, but it's been awhile since we had to make those comparisons when we were looking for windows.

Assuming you are talking about double-hungs and the tilt-wash instead of the narrowline Andersen 200, neither of these windows is a true vinyl clad wood window.

The Andersen has a vinyl clad plywood frame with a wood sash painted with a tough polyurethane paint. The Weather Shield ProShield is a vinyl window with some interior wood trim. The appearance of both is poor especially the smaller upper glass size in the ProShield model and the glass stop in the Andersen. I don't believe either one offers an applied muntin/grille or a sill that can be waterproofed without adding a subsill (not that there are many clad window that do).

I would be looking at all-wood windows or the Andersen fibrex or the Marvin fiberglass windows instead of these developer/builder grade hybrids.