I have about 70 GI surplus mags. Most of them were used and just given to me. I changed all the springs and followers with new ones and have yet to have a problem with any of them.
That being said, I am very impressed with the Pmags and Troy battle mags. I think they are a vast improvement in design and function. I will probably pick up a few, 20 or so, of them to add to my stash. Im kind of a magazine horder.