We decided instead of an excursion in Catalina (water was too cold for snorkeling)to rent a golf cart and explore the town of Avalon. 1 hour is all you need to see everything and still have time to stop and takes pictures. $40 for the hour was well worth it and there are at least 3 golf cart rental places right on the main street.
You can wander the downtown section of foot- lots of little cafes and restaurants as well as tons of gift shops. There is a pretty little beach down at the marina where you can sit and eat ice cream and watch the seals. We loved watching them and even had a few dolphin sightings.
If you are going in the late spring or summer I would encourage you to do some of the water excursions-we were not prepared to love the quaint town of Avalon so much and wish we had been there in June or July to really experience all it has to offer.
In Ensenada we decided on a whale watching tour instead of the winery, town or blow-hole tours as my husband was not interested in any of them. Unfortunately Carnival did not offer this option but I had done my research and was able to find the sports fishing pier and get us booked onto a boat with Sergio's. While we enjoyed the trip and the crew for the price ($80 for the 3 of us), it really was just ok. 4 hours is a long time to be out whale watching...
I wish we had done the combo tour of the city and the blow hole that Carnival offers as we really did not get to explore the town very much beyond the shopping area.