Settlers of Catan Expansions

Has anyone played any of the Settlers of Catan expansions - Seafarers, Cities & Knights or Traders & Barbarians?  We're getting a little bored with the original version but are not sure which expansion to buy.  Any recommendations?  Thanks.

Seafairers!!!!!

After getting this expansion set we never went back to the original island, instead we'd play the "uncharted territory version, where we could sail out and discover new lands.

Knights and Cities is quite a bit more complex - more things to keep track of. I think I may have played the barbarians one once? I can't remember.