Mine is exactly the same size as the European 6 button controller.
I remember getting the 6-pad Genesis controller as a kid and being blown away. It felt so comfortable in my hand, the d-pad was awesome and it had more buttons. The 3-Button controller was mediocre in its heyday and flat out obsolete the day the 6-button was released.
I think it's super lame that in the U.S. and U.K. they didn't make the 6-button controller a pack-in with the redesigned model 2 consoles.
I find the 6-button a little too small, the 3-button controller is a better size. Either way, one of my favourite controllers.
And for the people shitting on the 3-button dpad: there are at least two revisions of the design which completely change the way the dpad works. I had some which were utterly horrible and then some which were fine. I can't remember the details of which is which (although I *think* the earlier version was the bad one?).
At least here in NZ, they started bundling the 6 button controller in model2 console packs around when SF2 came out.
I'm honestly partial to the GCN controller, despite the garbage D-Pad and the C-Stick being an awkward second analog.
I've always found that big A button on the NGC quite problematic. Sometimes it doesn't respond as quickly as you need because you need to press it at its very center...