The Julius K9 harness is thicker- heavier duty- than the Brilliant K9 harness. The Brilliant K9 harness is also a bit smaller and thinner in the panel section, so it will be a cooler harness in general. Really, you can't go wrong with either. For a large GSD, I personally prefer the look of the Julius K9 harness. For my smaller Mal, I liked the look the the Brilliant K9 harness (though I didn't end up getting that brand for him).
C-ATCH Pimg - DOB: 2/06, RATO, UJJ (x2), DJX, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014
RATCHX2 High Jinks vom Neuanfang - DOB 9/12 (Gotchya Day: 1/23/2013) DN, CA