I have the Cuisinart Power 5-Speed hand mixer and I like it a lot. Obviously, no one knows what is the "best" hand mixer, unless we have used all the hand mixers on the markets. Most of us probably have only used a few. I did do some research, and the Cuisinart ones look to be better than many others -- at least on paper.
The 7-Speed mixer obviously have two more settings than the 5-Speed mixer (the one I have), but it is probably not any more powerful since the two models are rated the same Watts consumption.