If your mag won't run in ya gun, your tricked out AR will be in your handsI would think Mags are like beer... no matter what your preference is... never turn down a free one.
Actually... i think it all depends on priority... i.e., where you put your money first. If you have plenty of money... buy the best of everything. Otherwise... figure out what you think is the most important item for you to survive and put your money there first. Over time, you'll get everything you need, but just in case time runs out... I'd hate to see someone die of exposure with a tricked out 15 in their hands.