I've heard that a few times that it is purely mission orientated, but at the same time I have heard personal preference goes a long way depending what's good to go in the armory and in-theater. Then again, after reading a book about the PF just as they were about to cross the border they were ordered to use L85's over their M4's. Bureaucracy. At the same time reading "No Easy Day", every issued rifle was customized to that operators specification whether it came to trigger pull weight or what attachments you used. Matt had a mixture of issued weapons from the MP7A1 to a HK417 (10" and 14") along with numerous pistols. You have your team equipment (team bag and lockers plus individual), your lists of what you're going to need for the job: recommended and critical. Your "go bags" are purely what you need to complete the job. With other bits of kit you can go to the civilian market. Then comes logistics, availability (stock), bureaucracy, mission, team and individual preference. At best you want inter-operable calibers (i.e. most of the team rocking 5.56) and at times AK's, so on, aren't used because of possible friendly fire issues. At the same time the amount of weapons that SF transition through whether it's for research and development (even going to the SHOT show and the like), testing and trailing to using it in Afghanistan, every weapon platform will have a process before it's used or even considered to be used hence why M4/M16 platform and other known and tested firearms are used more widely by the community; never mind the fact that it is a training platform too, what they have known since basic on up. It's easier therefore to transition to a C8 or a SCAR rather than to a bullpup or exotic weapon. But as you say the best weapon is what you have in your hands, what you are using at the time. The true weapon is inbetween your eyes. "All weapons, one mind".
CQB-TEAM Education and Motivation.
"Pragmatism over theory."
"Anyone with a weapon is just as deadly as the next person."
"Unopposed CQB is always a success, if you wanted you could moonwalk into the room holding a Pepsi."