Armstrong does get a stainless primary in the 90, Lennox doesn't. Why not? Too cheap? Seems to me there's nothing builder about Armstrong when it uses better materials than the big name. Besides, parts prices will be SO much less than Dave's after warranty and support for non dealers is great as well.
Armstrong has a 95% 2 stage variable in up and down. All Armstrong 2 stage let you use a 2 stage stat for best control.
Goodman does have them beat in the warranty dept.