Something as seemingly innocuous as a buffer tube probably gets ignored by most shooters. After all, it is just one simple component, and they are all virtually the same. If this is your belief, then you probably shouldn’t be building your own rifle. If instead you understand that value of a good buffer system, you might check out this PWS Enhanced Buffer Tube Mil-Spec AR-15 / M4 as a top option.
Built from 6061 aircraft-grade aluminum, this enhanced buffer design was built with longevity in mind. It eliminates the need of a castle nut by using a unique indexing screw and plate system, which helps to ensure a perfect alignment in the weapon. The extended lip effectively eliminates carrier tilt, improving overall control of the weapon. The tube is also fluted to ensure that debris can quickly be cleared.
When you are looking to build a new rifle that will really deal with whatever you throw at it, this is a great place to start.