For 5.56 guns, my standard answer is an M16A1 flash hider. They are cheap, and work well. Your 300 is probably threaded 5/8x24, so the cheap A1/A2 option isn't there. I have a DSA three prong on mine. It works well, and the cost is reasonable. If you're looking to spend a lot of money, or want one of the designer muzzle brakes, I'm not the guy to ask.
The AAC muzzle brakes are awesome if you can get a hold of one with the 7.62 thread. The blackout is also fantastic.
Are you planning on running a can now or ever? That should be your biggest concern since most quick attach silencers use a proprietary mount (I stick with AAC so I can silence anything I want). If you're NOT planning to suppress the rifle, Noveske's flaming pig flash hider is the best thing since sliced bread imho.
My preference was a linear comp like the kies blast master (or Troy Claymore, Levang style, etc.). Recoil & muzzle flip are pretty minimal with the 300Blk so a focus on redirection of pressure and noise down range seemed appropriate.