I would always do cardio before yoga. Here are my reasons:

Cardio leaves the muscles warm and a warm muscle stretches and relaxes far better than cold.
After cardio the muscles can be a little tight, but are warm, so it makes sense to do yoga to relax muscles back out and also to help any toxons to be flushed out of the muscles.
Yoga after cardio helps the whole body to fully relax and there is nothing better than to come to the yoga mat after cardio and stretch and come right down to Shivasana to round off.

I think the other way around, yoga will leave you stretched out nicely but this is a bad idea for then doing cardio after as joints are more open and a danger of twisting or pulling muscles if they are too relaxed.

And Shivasana is a way for me to say, "there - it is done". Then I go get a nice hot shower and I am at peace in my body and with the world.

I've tried both before and after. Prefer to do cardio before yoga for all the reasons stated in previous posts.

Cardio after yoga wasn't fun...breathing was more labored, legs felt like lead, couldn't wait to be done; whereas after yoga I want to stay in that state of "bliss" for as long as possible.

I'm kind of a switch hitter. I usually do yoga after, but I find if I do three or four energetic sun salutations and/or jog in place for at least a minute as a warm-up, yoga feels just fine even if I haven't done any real cardio.