If you are looking for a really good upper assembly for the cheapest price out there, The Aero Precision Upper M4E1 16” 5.56 Mid-Length is probably the way you want to go. Purchasing it and testing it, there are some things that make this automatically one heck of an upper.
It has a very soft shot with its mid length gas system and is highly customizable with itws M Lok handguard features. I haven’t had any problems with fitting any kind of attachments I want on it. From Lights to foregrips, pretty much any accessory is a green for go.
The main reason I bought this upper is because I didn’t have to go through the hassle of assembling my upper. Sometimes, it’s just better to have it made by a professional.