It depends on which MAC formula you're talking about. I don't mind purchasing MAC lipsticks since $15 isn't too expensive (other high end brands are near $30) but here are my favorites.
If you like Lustres, try Revlon Super Lustrous, Maybelline Colorsensational, Rimmel Lasting Finish
If you like Glazes, try Revlon Super Lustrous
If you like Cremesheens, try Revlon Colorburst, Revlon Lip Butters, ELF Essentials, NYX Round Lipsticks
If you like Amplified Cremes, try Covergirl Lip Perfection,
If you like Mattes, try Wet'n'Wild MegaLast, Revlon Matte
If you like Satins, try ELF Mineral Lipsticks
This is based off each level of pigmentation, the texture, and moisture. HTH!!