I've been using the Logitech Performance M950 for the past month or so now.
Ergonomics wise, it is great for a right hander. With customised buttons via
SteerMouse. As I came from a Mighty Mouse, great mouse, stupid trackball. I needed the shortcuts I could get with the MM (Expose functions).
Also, I needed the sidescroll capability.
Looking at retail stores in Singapore, I found it overpriced. So I looked online and found cheap ones on eBay. Granted they MAY not be brand new, the mouse still works great and I got mine for less than half the price here. I'm a heavy user, and mine lasts on average for about a week. I use Sanyo's eneloop and rotate between 2 batteries. Great buy. YMMV.
I initially started looking at the Magic Mouse, tested them in Apple resellers around Singapore, I didn't like the low profile and it just didn't seem right for me.
I use a MacBook Pro and getting an external trackpad is out of the question.
Hope you'd find the right mouse for yourself.