I've never tried greenies, but the BIG Dentabones last my dogs about 10-15 minuets.

I know I laughed at the package when it said to feed them 1 or 2 a day.. YEAH RIGHT!! Those things are $$$$$!

I give them to mine about every other week. Their teeth are clean as it is, and they don't have a problem with bad breath either. So I don't have to give them to the very often.