Wasr 10/63s, even regular wasr10s.
And still lots of Beprs out there (easy conversion)
I've never built anything, but I can see the reasoning. You can pick something not currently being produced, and know what you're getting with some of your own hand-picked components. When WASRs were $400 I don't see it, but when a 10/63 is near $800 I could see why someone would just rather build. (and pay someone to build)