Re: quality stripped lowers?
A lower is a lower as long as it's machined to spec.
Some offer additional features (i.e., built in trigger guards, ambi bolt/magazine releases, upper tensioning screws, etc.), so if you feel like you need something like that, then go for it.
I would say the lower receiver is one of the least important features in a build (once again, as long as it's machined to spec). You are better off spending money on a trigger or barrrel.