what is best audio connection for dvd to receiver?

The digital outputs (optical/coax) are for sending the DTS/AC-3 surround code from the DVD's to the surround decoder in your HT receiver.

If you are playing regular music CD's the analog outputs are what you are using, unless you are using a separate audio DAC (digital to analog converter) like the MSB Link DAC, (and others, etc), in which case you would also use the digital outputs..

As far as optical vs coax; most people prefer coax; however, if you really want to know what works best for you, then you should really try it both ways yourself. The cable used can have a large effect on results..

Sugarbrie,
I don't mean to contradict you sir, but I think your 2nd statement regarding "regular music CD's" is not completely correct.
Most (all that I know of) receivers (and pre-amp/processors) will play a regular CD through the digital outputs. You'd simply have your receiver/pre in 2-channel mode. The receiver/pre would be doing the same as in surround mode....simply receiving the digital signal from the DVD player and processing it according to how the receiver/pre was set....in this case for 2-channel/stereo.
Now I THINK I'm correct on this one (and I had a couple of beers with my friend earlier!) :-) so please kick it back to me if I'm wrong. Either way....we all learn something and that's the idea!
Happy Listening!

P.s. In COMPLETE agreement with your last statement regarding Coax!
Happy Listening!