well you can get a flat top (with removeable carry handle) 16 inch barrel nextyou need to decide weather you want a full length hand guard or the mid-length most likely with a 16 inch barrel you will want the mid-length
now are you set on a 16" barrel or are you debateing between that and larger sizes ? i have an 18 inch barrel and i like it alot i like the looks of the longer barrel. also do you want the regular hand guard or the free floating kind?
this is the flat top with the regular hand guard
this is the one with the free float tube the free float hand guard is supposed to give you a better accuracy i think but i doubt that much so i would choose which one you want by which one you think looks better
the top two have a gas block with a rail that you can put a front sight on if you want. this one has a perment front sight so if you put optics on it makes it hard to see it can still be done but its not ideal. now with the top two you CAN get the detachable carry handle and a front sight also on the plus side you can get flip down front sight so when you throw your optics on all you have to do is flip it down and its not in your way but with the bottom one you would have to remove it. now the bottem one has the permenent carry handle but mine has the flat top with the permenent front sight(which i will swap out when i get the money)
i would say the best choice is one of the top two with flip down front sight and a detachable carry handle. also there is the choice of if you want a stainless bull barrel which is more accurate but not as durable
or a regular crome lined or non-crome lined steel barrel which is less accurate but will last longer. even though chrome lined is less accurate i would recomend it since it will last longer it all depends on what you want/need