First post…incredible amount of information you guys have here! Great site! Yes, I’m yet another new guy in need of advice. Never thought I’d want an AR <fast forward> now I’m in the middle of my first AR, and I’m like a kid before Christmas.
After many Internet searches and lots of reading I decided to “build” my first AR instead of buying a complete rifle. Ok…“build” is stretching it, maybe more like buy a complete upper and complete lower, and “say” I built it 
I’m funding it by selling two pistols.
After reading glowing reviews, finding “the chart”, and selling my first pistol, I ordered a complete BCM mid-length upper (standard barrel, BCM BCG, and standard charging handle). I think I made a good choice, if I do say so myself.
Now, how to complete the “build”? I think I’ve narrowed it down to either a BCM, LMT, or Stag Arms lower. I can save a little money with the LMT, and even more with the Stag. Also, I really want a Magpul CTR stock. The BCM and LMT come with a “standard” carbine stock, however I found a place that I can get the Stag lower, LPK installed without receiver extension, buffer, stock, etc… So, with the Stag I could put the stock and buffer that I wanted.
Questions:
Are there differences in a lower’s quality from BCM, LMT, and Stag?
Is there an advantage to sticking with all BCM parts?
If I go with complete LMT or Stag lower, I think they come with the “carbine buffer”, is it ok to run a carbine buffer in a mid-length rifle? Is the H buffer better for mid-length rifles?
Thanks!