There are some adjustable stocks that are solid. The magpul with the friction locks can be pretty good. My personal favorite is my LMT sopmod. Zero movement on my vltor extension. With that said, I like fixed stocks. Only difference is length, with A2 stocks having the spacer and being 5/8" longer. I prefer A1 personally. I use Cav Arms C1 stocks on 3 guns and like them a lot. I've used a VLTOR fixed modstock and liked it a lot. Its light and looks cool with options for sling points. I've also use an ACE skeleton stock. Super light and uses the buffer tube as part of the stock. The MAGS EFX stock looks cool and I'd like to try one out. Couple guys in here use the magpul with good results. Another option if you want to keep it short Is an entry length stock. Lots of guys use them in conjunction with a 1" spacer and say it's about perfect.