It depends on the gun brand and the luck of the draw.
I've had good luck with S&W 59 series Pro-Mags. Also with some Pro-mags labeled as "EAA Factory." Pro-Mags have also worked well with most of the CZ compact guns. I use the 75B Compact .40 mag in my 9mm Compact -- gives me four extra rounds! (The only cavaet I can offer is that the springs will not live long, and you'll have to replace them. But for the CZ compacts, the Pro-Mag price of around $13 compared to $30+ makes that an easy decision.)
Pro-Mags for some other guns are crap.
The nice thing about Pro-Mag, and unlike some other makers, is that if you have problems, Pro-Mag will generally try to make it right... and will sometimes throw in extras as freebies.
But, if you can find Mec-Gars, that's the best way to go. The price will vary from a little more $ (for some guns) to a LOT MORE $, but they are great mags (and the OEM provider for most major handgun makers.)