I have no immediate preference - it all depends on the individual comic.
Some artists are amazing at black and white, and the comics they create use that super-effectively. Others work miracles with colour. It all depends on the end-result, really. They both have their individual strengths and weaknesses.
I've drawn comics in every part of the spectrum - full colour, limited colour, greyscale, purely black and white linework, etc. - and I've made those choices based on time-constraints, style and content.