If had to choose between the two, I'd go with Steampunk, but in all honesty I prefer a good mixture of Steampunk and Cyberpunk, like in in Warhammer 40K.
Obviously a lot the technology is very Cyberpunk, with people having cybernetic implants, people being linked directly to their vehicles etc, but the aesthetic design of a lot of the technology is very Cyberpunk, with lots of brass and skulls, brass computers or logic engines which have ivory keys like typewriters, and which load programs via punch card readers and display their results on ticker tapes.
Also despite their advanced Cyberpunk technology, they have a rather Victorian view of it, regarding it as magic, only understood by Tech-Priests.
I think the Warhammer 40K universe was Cyberpunk during the Dark Age of Technology, but has since regressed to Steampunk after the Age of Strife.
This is the impression I've got from reading a lot of the novels.