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Depends what you want. If you want just standard 5/30 mags, anything by Magpul is solid. USGI's work good, lancer mags are fine but are expensive and don't offer anything better over the latter.
Personally I find the poly mags to be somewhat unreliable when it comes to feeding. They quite often jamb. I like the the metal mags. I have the original 5 round Wyndham which works great plus two other types LAR-15 mags which also work like a damn.
My uncapped works ones! OR
USGI for long term reliability, functionality across the board, weight savings, cost. Add in Magpuls to smooth out the edges/better grip