Since your experience with an M16A1 back in your service days, a lot of things have improved markedly!
A lot of parts and Magazines in particular have improved in quality.
I built my first AR15 back in 1987 in basic AR15A2 form with an FN Match Barrel for use in DCM, now CMP, Matches and some general plinking.
Now after many years of use, I'm going to replace it's barrel, which although still working, has lost a good deal of it's accuracy edge.
I'm also tempted to free float it's barrel.
While it's very tempting to further modify it, I may just build a whole other Rifle, and I've built quite a few other AR's for friends supplying their own parts.
AR15A2 HBAR built on PAC West Lower with 2x Scope and Enterprise Arms Muzzle Brake. Bolt has 3 layer Gas Continuous Gas Ring.
In building another Rifle, I'm leaning towards possibly going with a Gas Piston Drive, depending upon finances.
A Flat Top Upper with a Free Floated Nitride Barrel is a given, so far.