The main difference between the two is that the black one has some rise to it as well as being swept back, so you'll probably be sitting a bit more upright with it.
What kind of riding do you do and on what kind of bike ?
My personal preference is for the black (comfort) bars which is what I have on my bike. I find them perfect in allowing my wrists to be perfectly straight.
I have a feeling that they also offer more adjustability for a comfortable hand/wrist position compared to the flat silver bars, but I may be wrong.