I'm not familiar with Small Cats, but would highly suggest The Silver Moon. It's a beautiful catamaran, wonderful service, food, experience. They take only a small number of passengers so it is not crowded at all.
Our group of 8 has chartered Small Cats for our excursion in Barbados in December. I thought their charter price was very good, plus we only wanted a hour snorkel cruise so we could have the afternoon free, and also have lunch on the ship. With transportation and drinks included, the cost for our charter was 450 for the 3 hours. I agree with others that the Silver Moon has received great reviews, but our group wanted a shorter cruise than they offer with the lunch. They do offer a shorter 3 hr. cruise, but it is on a power boat. I felt their charter price was more than we wanted to pay.
I have also been in touch with the West Side Scuba Centre, and they were very responsive to my emails. They also have charters, as well as lunch and no-lunch snorkel cruises. Smaller catamarans, similar to Small Cats.