If you do HEAVY yield printing, go with the Sharp because the cost per page won't obliterate your wallet. The downside is that the Sharp AM-900 is a Black & White only machine.
If you like to do color, or photos, or <moderate yield printing, then go with the Epson RX500. I've seen the RX500 in action and although it's a bit on the slower side, it does an excellent job in the quality department. I would not recommend the CX6600 because it uses Durabrite inks for photos and from what I've heard, it isn't "true" photo ink.