Stay away from those cheap "USA Brand" magazines. They are not reliable whatsoever, as they misfeed and doublefeed all too often. The new Bushmaster 10 rounders are no longer "frankenmags" and are probably the most reliable 10 round mag avaliable. They cannot be disassembled however.
My suggestion would be to invest in a few Thermolds. They are made from a durable plastic and wont scratch your magazine well. In my opinion, they are also the best looking 30 rounders out there.
Orilites are also a good choice, but you may need to do a little research before you buy. Some have a low melting point, causing the magazine to deform during rapid fire. Orilites also need to be slightly modified to fit into a Bushmaster. Nothing complicated tho.
USGI/Colt magazines are also an excellent choice. They are mostly sought out for their name, as some of the older ones are rather valuable. It's a good idea to do a little research on them. You can find alot of "treasures" at a gun show if you know what to look for.