I have the SA M7S. It's a fixed-stock, milled 7.62x39, and solid as a rock. Have shot it regularly about a year and a half, probably several thousand rounds by now, and w/out any problem of any kind. Still looks and feels basically new. Has showered abundant valor and glory in several local matches.
Mine is a post-ban version that came with a pinned comp, but which works great not only re-directing recoil but also supressing flash.
I also briefly tried the underfolding SAS M7. Basically the very same gun but with the folding stock and without any muzzle treatment (although it was an after-ban threaded). Looked muchos
[email protected], but definately more recoil rise, and the folding stock forced me to crane my neck further to align with the sights, which I was uncomfortable with. I sold it after a couple months and a few hundred rounds, deciding to retain the fixed-stock SA M7S as the keeper. You might not have the same problem though.
I don't think you can surpass any of Arsenal's stuff quality-wise.