Not a good time to buy right now, prices are crazy! Ruger works the best, I also have Promag 20's that work. The plastic mags are hit and miss, newer rifles seam ok with the generation 2 Tapco. All the sites I have looked at are out.
I got a few 20 and 30 round metal unbranded magazines that came with the used Mini-14's we bought. So far they work great but the only thing I'm seeing is that the sheet metal is soft and where the front latch pin hole is if I don't get it perfectly aligned before pulling them into the latch the area around the hole bends inward. I highly recommend using Ruger factory magazines if at all possible because their magazines are made of a harder material making them a quality product far less likely to give function problems than aftermarket magazines.