For a ‘scratch’ build, I like the Caspians. They’ve been the highest quality for the price.
The Essex frames are okay, but not a well done.
The Wilson Combat’s, STI’s and such are just too expensive for most people.

In a built ‘builder’ gun, I consider the Springfield Armory Mil-Spec the base or basic model to get.
Anything less needs too much work and too many parts to fix.

I prefer to build on Colt’s when I can, the quality is about the best across the board right now.
Some of the 70’s series guns were sketchy but since the 80’s the quality has really come up.