One it depends on what you are going to use it for. Do you plan on putting a scope on it? I just got a Stag Arms M4. It has the removable carry handle and has an integral weaver style mount on the upper. super high rings are needed to install a scope sosighting won't be interfered with by the front sight.
However if I decide to take the scope off and reinstall the carry handle, it can be done in under a min.