Worst F I know of is 19" wide with an armrest. The best E I know of is 18" wide with a shared armrest. I'll take the width any time.
Actually, the worst F in the U.S. has 18.5 inches (AA, DL, and HA):
http://www.seatguru.com/charts/domes...rst_class.php#
Singapore and British Airways have wider economy seats:
http://www.seatguru.com/charts/intl_economy.php
That's before one starts to talk about service . . .