-20 inch barrel
-A2/A4 buttstock (quality)
-Quality receiver, handguard, trigger assembly, etc..
-For a barrel, get a stainless/fluted barrel. You will marvel at the advantages.
-Get a 1:7 only if you plan on shooting heavier bullets 68-79gr. If you'll be shooting 55's or SS109's, get a 1:9.
-Stainless over chromed lined. Better accuracy.
-A2 buttstock is good.
-If you want QUALITY, get a VLTOR billet receiver. Must stronger and helps with the harmonics on heavy/long barrels.
How much do you want to spend?