SPDIF vs. AES/EBU Sound Quality?

Yes, IMHO AES/EBU will provide the best quality up to 24/192 kHz and single rate DSD, for higher sampling rates you'll need USB or I2s.

I've never compared it to I2s but it's been better than USB in every comparison I've done.

The cables are never the same but there shouldn't be any difference. That doesn't mean there won't be 

+1 those are inherently different cables.  How that effects sound will depend on what you are connecting the Lumin to.  If for example their S/PDIF isn't well implemented, relative to AES/EBU, then there will be a difference.  Not being a Lumin owner, I can't comment

Here is some information on the topic.

I have liked the sound of AES/EBU over SPDIF when inputting to previous DACs I have owned but different DACs use different input boards, some better than others.  My current Mojo Audio DAC is optimized for best performance from the USB inputs and my former Metrum DACs were optimized for I2S, so I used the optimized connections with each of those DACs. 

One reason AES/EBU may sound better with some DACs is discussed as point #2 (below) in the linked article.  I wonder if this may make the quality of the AES/EBU cable less critical than with SPDIF cables?

2) AES/EBU uses uses ten times the signal level of SPDIF, meaning it can tolerate more loss in long cables and if a receiver circuit has been optimised for AES/EBU it will work better as SPDIF will be at the lower limits (too much noise)

SPDIF unless terminated in proper 75 ohm BNCs, is my least favored way to move a digital signal. AES works well, and I have also been quite satisfied with USB 2.0