Nude Or Black

If it is one or the other, my advice is keep the lighter colored pair. A dark line across your ankle will make you look shorter, even though lots of people wear black ankle straps. Also a "nude" color will be easier to wear both day and night, so you will get more use out of them.
You asked if they are comfortable, they don't look too high, so I would imagine they would be. They both are beautiful shoes!
 
I don't have that exact pair but a similiar style and find they cut in around the foot a bit.. but for CLs they do look shorter so would assume they are higher.

For me, I would probably go with the black. I actually like strappy shoes in black as I find it looks sexy. I do love nude CLs but prefer them in pumps as the look is so sleek. So for me, I'd stick with the black. I have lots of shoes in black with ankle straps and I just love em!
 
They are comfortable. I don't know the heel on this, 85mm? I have the Balia Spike a version of the Riveriena in 100mm. My sister has these in black. Upon consideration of BalenciagaKitte, these might be pretty nice and work quite often as a neutral tan shoe. Good luck.
 
I love the Louboutin nude but I find it difficult to match with my other "nude' bags/ clutches because of the pink undertone I wish I had kept that in mind while purchasing my PF's. That and their black patent is so shiny and luxurious looking. Both are beautiful though, you can't go wrong.
 
I agree with BalenciagaKitte, the nude is way more versatile and leg lengthening and Louboutin makes the prettiest nude color. Blake Lively wore these in pale pink to a premiere and she looked gorgeous.
Blake-Lively-Cafe-Society-Christian-Louboutin-3.jpg