Well, no one can tell you what is best for you... we all have to go thru a learning curve. For starts, it is tough to go wrong with a Hartford Horsey or a RRA.
I'm not saying this is ultimate or best for anyone, but I love it:
My rifle has a mid-length gas system, 16" barrel, and a 20.75" sight radius. LMT CQB16 with my modifications.