Depends.
When I worked at Radio Shack and interviewed at Whole Foods the manager asked me why I wanted to work there. Told him it paid more and I could walk to work instead of bus. He cracked a smile at the answer. Next question (this was post college just after the dot-com bubble popped) "If you find something in your field are you going to leave?". Told him I almost certainly would leave if I found a job in my field but until such time I will bring my A game to doing this job. Guy totally appreciated the honesty, he told me later he was going to pass until I didn't beat around the bush. It all worked out pretty well.
More recently as a professional (left Whole Food to get back into my field just like I said I would) I have also been honest but with a bit more polish. Once my motivation was mostly pay and I mentioned that along with "and I think the position sounds interesting, you are doing neato keen stuff, etc". Next time I was looking I wanted to move and I basically laid that out as well. In those cases I got offers every time that question was asked.
At the end of the day IMO honesty is the correct move. Feel free to demonstrate that you researched the position or at least have been listening while the position was described in greater detail but don't hide the fact that you want more money, less stress, better bennies, whatever.