I've wide feet, and these are the best of the slip on shoes that I've tried (and I've tried many different brands). They run a bit narrow though. My measured size is 2E, and the 4E fits reasonably well for normal wear (the 2E would be too snug).

HOWEVER, I bought the shoes for airline travel, and by the end of a long flight, my feet have swelled to the point that the shoes are quite snug. I'd suggest getting them both wider than you expect and a half size larger if you're using them on an airplane.