In terms of shape, I actually didn't mind the Mighty Mouse at all. It was the buttons (or lack thereof), which made it horrid. Also, since there were no dedicated buttons, it wouldn't know with which finger you were clicking with if you had both fingers lying on both sides, so it would just register the left click if you had your fingers lying on both sides. This meant that you had to consciously lift up the left finger whenever you wanted to use the right click. This was horrible for gaming.
As far as contemporary examples go, in terms of shape only, the worst mice are all the gaming ones from Logitech. G700, G9, G400, and new the G602 are all terrible. I have no idea why they insist on having so many odd curves and angles on all their freakin' gaming mice. It's as if they are suggesting that all of those curves and shapes are required for comfort; it's obviously a marketing move. But in practical use, all those curves and angles make their mice super uncomfortable. You are absolutely forced to hold their mice in one very specific way, but again, in practical use, people need the freedom to hold their mice in different ways and angles; because everybody's hands are different, and the mouse is constantly moving. Why do they think holding the mouse in one very specific form is appropriate, when the hand is required to constantly move to move the mouse, I don't know.
That said, I will say Logitech mice are the best, that I've used of course (there may be other brands out there that I haven't used that may be better), when it comes to build quality. All their mice just feel super solid, and I've never been afraid that one would break over a period of time.
With THAT said, when it comes to quality... I'll agree with everyone, that Razer is absolute ****e. Almost a third of Razer mice I've owned/tried, had issues with a weak/flimsy/creaking body. They just feel... hollow, and all the pieces feel weakly put together. It's a shame, because I absolutely love the design of their Deathadder and Taipan mice.
To me, it doesn't really matter how well built a mouse is, if it is super uncomfortable, so I just deal with the build-quality issues of Razer mice, and just use Razer mice. To me, personally, I think it's easier to just deal with and/or replace broken/lemon mice from Razer, and continue using new ones, rather than having a really well built mouse that I can barely use (Logitech). Because in the least, I can still at least use the mice (from Razer).
Yes, I know I'm bitter about Logitech mice. I have just given them way too many tries, and every single time, I'm unsatisfied with the shape of their mice. I want to like them... but after a certain amount of time, they just get put back in the drawer, or returned to the store. I guess that's a part of my fault, so... no more Logitech mice for me. Unless I see that they change the way they design their mice.