When I visited New York a couple of years ago I bought a wired keyboard for my Mac, not realising there would be any significant difference between UK and US keyboards.
As it turns out I actually prefer the US keyboard.
My friend Mike was asking me about the differences between the two keyboards so I decided I would demonstrate with the following picture:
The UK keyboard is on the top and the US keyboard is on the bottom. The UK keyboard is wireless, so that's why the keys are squished together in places.
To get the meaningless differences out of the way first: Since my region is set to 'UK' the 2 and 3 keys (highlighted in yellow) behave the same no matter which keyboard I use. I don't recall ever using the extra key on the UK keyboard, highlighted in orange.
The biggest difference for me is the location of the backtick key, shown in pink. ⌘ + ` is the key combination to switch between windows within the same app. On the UK keyboard this key is too close to the shift key, and means left shift is tiny. On the US keyboard it is in an ideal location, above the tab key.
Lastly is the return key. On the UK keyboard the key is vertical while on the US keyboard it is horizontal. Since my fingers move left to right much more than they move up and down having a vertical return key is like building a runway that is wide instead of long.