Re: AIMPOINT COMP3 OR COMP4?
Being the tech geek that I am, I have to throw my hat into the M4 corner. Actually, I like the M4S, with the lower battery compartment. The M4 has a much longer battery life and runs off of a AA battery, which is just HUGE. You can find AA batteries anywhere, and 80,000hrs of usage is 8 years.
The major bonus to the M4 is that it utilizes an integral mounting system, as opposed to the M3 which mounts by 30mm ring attachment. As a result, there is no chance of scope cant, so you know your zero will be more reliable.
In terms of QD mounts, it's not a big issue if you use the proper mounts and check them occasionally. The QRP mount that Aimpoint makes is actually very sturdy and durable. I just don't like the large knob on the side. Instead, I would opt for a LaRue mount, but that is just my preference. Most mounts from reputable companies are reliable and durable. The M4 warrants a QD system, based on the mounting platform design. The only systems that I detract from are A.R.M.S. mounts, since the levers are not very durable, and they're held in place by a roll pin.
Another option is the T-1. I run a T-1, and it's a fantastic optic. It's also incredibly light. There is literally no top-heavy feel to the rifle. They're just as durable as the other Aimpoints, and the battery lasts 50,000hrs.