I vote for cardio before, even though I am sure it is just a matter of preference for everyone. My legs just feel like such jello after GS legs that I really don't get much benefit out of my cardio. I do my cardio after GS BSB and GS CT though.
I know that I hear it all the time to do strength training first...but that has never worked for me. If I were going to do both in one day, I'd do cardio first also. That just seems to work better for me.
It really depends what your goals are. If you are looking to get the full and thorough leg w/o, i would not do cardio first. if cardio is your main focus, then do that first. it really all depends.
Here's another one.I do cardio everyday and do Cathe's leg workouts without weights (freestyle). If I'm working out back to back, I do the leg work first and if I'm feeling shaky or tight, the cardio loosens me back up and cuts down on the DOMS. I have had tremendous results with this. But as was said it's everyone's own preference.
Hope ya figure something out you like.