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BT Mighty Mouse because I already had it.

I have tried the Magic Mouse and just can't deal with the fact that it doesn't have a center click (button three, click the wheel, etc.). I use that ALL THE TIME to open new tabs in Safari/Firefox. I love the swipe gestures, but no center click is a deal breaker for me - I'll never have one as long as there's no button 3. :(
 
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