Digital is digital but HDMI is probably a more elegant solution from an aesthetic point of view.
If you are using HDMI and your HDMI sound card is able to support multi-channel PCM, you have the option to decode in MC or to bitstream and let your receiver decode the audio. By decoding in MC you gain a wealth of features that probably aren't available on your receiver (like videoclock, convolution, room correction, etc). However, some people like to let the receiver do the work and that's fine too. SP/DIF requires bitstreaming of multichannel soundtracks and also doesn't have the bandwidth to pass the newest HD Blu-Ray audio formats.