I am no expert.
Why lose the Mini-14? They are great little tools that will last longer than most of the plastic guns around. The rifle has been around for many decades and is still a very strong competitor. Besides, I love the wood stocks!!!
That said, the Ruger SR-556 has a very good reputation. I also personally like the Core15. Sig has a good reputation as does FNH, HK, SCAR, Colt, etc.
The Core15 gas impingement happily ate the really cheap steel cased ammo, spit it out, and asked for more! Behaved very nicely. Also accepted a very cheap magazine without issue as well as pmags.
Read alot about piston guns. There are pros and cons. From my reading it appears I would never want to buy an entry level piston gun due to issues they may have of becoming loose after a 1000 or so rounds of shooting. Again, I have no real world experience just internet quarterbacking from reading around the web.
What about gas impingment systems? They will run less money and can run quite well with tonnes of rounds through them.
I would also peruse the used guns sections of everywhere. What brands are prevelent on the resale market? Might there be a reason for this? Which pieces can you almost never locate used? Why might that be?
Hope I have given good food for thought.