What do you like listening to? What speakers do you have?
I choose the Onkyo sr600e. Concerning connections (lots of (S-)video inputs), possibilities (component video switching), remote control (learning), build quality (very solid) and power it's clear the winner. Concerning sound I think they are both very good although the 600 has 24/192 dac's for stereo sound. Furthermore the 4300 is much cheaper (although in the Netherlands). A better match with the 600e is the Denon 1803.