I have both and find myself using the corded version much more. The cordless is nice for small quick projects where you don't feel like plugging it in and situating the cord, but if you are holding it for intricate projects, it can tend to be a pain as it will wear the small hand muscles out. I also have the flex-shaft extension, found here
, which is probably one of the best attachments I have bought for it. It allows me to get into tighter spaces and doesn't wear out your hand if you are working on something detailed.
Edit: I also agree that it's worth the extra bit to get variable speed.