Agree Paleo by boat is a great trip. The San Stef Travel trips to Ericousa or Othoni also v. good. Ericousa is really beautiful with an easy walk, Othoni also v. nice. For something different, Albania is worth a trip and would really recommend the Parga and Paxos trip. both these are a long day but worth it.
Of the coach tours, have only done the SS travel Corfu Town shopper. It's a little more expensive than the local bus but you don't have the slightly chaotic wait at the bus station for the return.
SS travel are cheaper than Thomsons and the girls will look after you. Enjoy.