HDCD and XRCD. Which's one sound better?

XRCD is not a format. It's a mastering process, or at least the brand name of a mastering process. HDCD is kind of a hybrid, but it does require a decoding chip to gain its full benefits. And its claims to technical superiority (as opposed to just good mastering) are open to challenge.

As "formats," neither will sound better than the other. If there are recordings available in both forms (I don't know of any, but there might be), either might sound better. I'd put my own money on XRCD, however, because JVC does really good mastering.

For the record: K2 Super Coding is what is used on XRCDs. It is not a separate process. For details, check out www.xrcd.com.

Garfish: I can't absolutely guarantee that an XRCD and a non-XRCD that says "K2" on it are the same thing. But I'd be really surprised if JVC goes to the trouble of doing two separate high-res masterings of any recording, given the low volumes they must sell of these things. And I can vouch for the sound quality of the Fantasy jazz recordings, which sell for a whole lot less than the XRCD versions and can often be found in retail outlets.