I use circular needles for all my knitting. They are much easier on the wrists and hands because, as the knitting grows, the weight of it all rests in your lap, suspended from the 'cable' part of the circular needle. Whereas with 'straight' traditional needles, the work is always on the needles, and your wrists/hands are compelled to carry this weight.
I also like circular needles because I never lose the empty needle! Ha!