Audio: HTPC to Receiver question

I’m wondering which option will give me better sound from my HTPC:

HDMI audio to my receiver OR optical SPDIF audio to my receiver?

My motherboard is a MSI K9N socket 939 that I’d use the SPDIF out on, while the video card is a HIS ATI HD 4670 PCIe.  The receiver is Pioneer Elite VSK-21TXH receiver.

Thanks,
Mike