Any ammo will be fine in your barrel. Barrels, however, are like snow flakes - to the naked eye they all look the same but there are microscopic differences that make them each unique. The only way to know which ammo your particular barrel likes best is to try a great variety and see which gives the best results.
Generally speaking, the more expensive rounds should be more consistent, as they have tighter tolerances for all things considered and most likely use better (lower flash, cleaner/faster burning) powders.
However, I bought a 5.56/.223 specifically so I don't have to pay $1+ a round, so I shoot the cheapest brass cased I can find. I'm mostly just target shooting/plinking or practicing where MOB is sufficient. Steel cased is fine to shoot, I'm just OCD about a clean gun and the steel stuff is so dirty.
My gun really likes the Winchester 5.56 55gr FMJ, but I also shoot a ton of .223 fiocchi, PMC bronze, and American Eagle cause it's cheaper and still gives me good, consistent results. I stick to 55gr because a scope I sometimes use has BDC for that particular round.
