There are so many options that work for different people that we could literally have a thousand page thread if everyone at MacRumors chimed-in.
I think Logitech are complete crap. Their Bluetooth technology is awful (search Google for all the people having connection drop issues with their products). The hardware is great for a year, but then the cheap plastic starts disintegrating (literally). But they are very comfortable and versatile to use while they last.
The Apple Magic Mouse can be incredibly uncomfortable due to its extremely low-profile, but it's also easy to set up, easy to use, versatile, very accurate, offers touch gestures, doesn't require using a USB dongle and will most likely outlast the Mac you're using it with.