Your BEST option is original russian. You can pick those up at rusmilitary.com. Kvar is supposed to be importing some soon as well. You're next best option is kind of a toss up between surefire and AGP. AGP's now come in coyote tan as well as black and have metal feed lips. Surefire's come in black and can be cut down to whatever size you want. If you want a drum go with MD Arms.
promags are horrible. There was a half assed fix for them by packing them with wine corks and boiling the whole thing, but it's not worth the frustration. You'll be happier with the other options.
I havent had a single problem with my SGM's (surefire), and have somewhere around 500 shells through them. I know its not alot of rounds for testing but so far they have been flawless. I only have the 8 rounders though, so I cant speak for all the sizes.
I run SGM (surefire) 10 rounders and have NEVER had a single issue. I also run a MDARMS drum and, again, never had an issue.
Grabbed the Surefires from Carolina (best price I've found) and the drum from Copes Distributing during their Christmas sale. Both places ship very quickly and take care of any issues very quickly.