I really enjoy writing both, but I have found writing historical is so much tougher than contemporary. It isn't the research but the effort it takes to make my voice appropriate to the genre. I need to "translate" my voice into a historically flavored tone. The vocabulary is different although I tend to keep the same sentence structure. Heroine has to be different as well. She can't go running around with 21st century sensibilities and I feel the constraints of keeping her mindset in line with the era she lives in.