Which is the better player Cary 306/200 or 303/300

I had both and I would say they sound about the same, but I would go for a 303/300 for more than likely you wont have any problems.
The older 306 had some issues. Do some research here on Audiogon to find out more about them. The latest 306 Pro series is trouble free though.

I own the Cary 306/200 and have never had a problem other than recently with some of the buttons on the remote control not working. It is I believe one of the best cd players ever made. It never ceases to amazes me with the quality of the sound it produces. I have never heard the 303/300 but I am sure it is also a very good player.

Disclaimer: I am currently selling mine to purchase a Modwright Transporter.

I owned a 306/200. I did an all out assault bought 5 CD players and a/b/c/d/e/f'd them all. the clear winner was the Ayre C5xe which has since been greatly improved with the mp upgrade. Eventually though I ended up with a Modwright modified Transporter as well and have never looked back. However if you're sticking with a new CD player I think you'd be making a mistake not to consider the updated Ayre.