The Cinelli logo on the XE is a sticker, whereas on the XA it's a drilled & recessed plastic button (looks much nicer IMO)

The XA's clamp is serrated on the inside for a better grip, the XE is smooth.

The expander-bolt retention mechanism on the XA seems more elegant to me than the XE's wedge-jam.

I've got a few of both, and the XA's are becomming VERY hard to find. The XE's may actually still be in current production, not sure.