I have used both.
IME Souveran is a very good wax. It applies and removes like melted butter which is nice. As far as looks, it leaves the paint unbelievably wet looking the first couple of days or so and then fades a bit but still looks pretty wet. It gives a good amount of reflection, but the reflections are not terribly sharp or accurately reproduced. Plus, it tends to mute flake.
Zymol Concours is also a great wax. It's not as user friendly though. The bare handed application can sometimes be annoying and if you have rough hands it can be bad for the paint. Someone on here once mentioned they warm applicators in an old toaster oven instead of using their hands. Also, you need to make sure you buff off excess really well. I've had problems with streaking in the past because I didn't thoroughly buff the car. A little QD usually fixes up the problem, but in the mean time it almost looks like holograms. As far as looks, it doesn't leave the paint nearly as wet looking as Souveran. It's more of a warm look than a wet look. However, reflections are unbelievable. The depth, sharpness, and color accuracy of Concours is really great. Plus, it doesn't mute the flake to the degree that Souveran does.
Personally, I prefer the look of Zymol but lately the ease of use of Souveran has been leading me to using Souveran more and more.