My favorite thing is a foot...my walking foot. I use it almost all the time and think I'd like to have a built-in walking foot (on my Bernina it's not built in).
I also miss the knee pedal. Like crafter005 I also learned on my mother's White (1947 vintage) with the knee control. I've had trouble learning to use the free hand system knee thing on my Bernina because I just revert back to moving my knee to make it go!!