A perfect trigger from the factory would take part of the fun out of this rifle! Any AR15 trigger set will work. The Rock River 2-stage worked wonderfully, but not that wonderfully to spend another $120 on a trigger for a $400 plinker/trainer.
The "15 Minute AR15 trigger job" works well and costs ya nothing. Likewise the JP yellow spring set which is a "drop in." I noted little if any difference between the two, but left the yellow springs in the rifle.
The stock disconnector spring in mine was "blue." The others, including the mainspring, are unpainted.
My trigger is smoothing with age.
Be careful polishing. The sear portion of the hammer and trigger are merely surface hardened. You can get a great pull, but can also take too much off and find yourself doing this again every few months.
-- Chuck