Sig 556
The SIG 556 has come down in price so it is a good choice. It provides AR 15 accuracy with AK 47 ruggedness and reliability
The SIG 516 is a great gas piston adaptation of the AR 15
If you are looking for a AR style clone the Spike’s Tactical is a high quality AR for the price as is the Smith and Wesson MP15
Best of all is the new FN SCAR 16s but it is a bit expensive at around $2K
In 7.62 the FN FAL or DSA SA58 FAL replica is hard to beat and highly recommended