My sister and I had limited time in San Diego while on a cruise but wanted to see as much of the city as possible. I'd been there previously, but not in a long time, and she never had. She'd had prior experience with hop-on/hop-off trolleys/buses, though, so were pleased to find that there was a well-recommended one in S.D.
Purchasing our tickets online was a breeze, and I was able to find answers to all but one of our questions on the website, and the other through a quick phone call.
We hopped on at the Embarcadero stop (conveniently adjacent to the cruise ship terminal) and stayed on the trolley to the Old Town Market stop, where everyone gets off (and where we met a friend). The full circuit takes about 45 minutes, so we were on for about 30-35.
Our tour guide, Vinnie, was excellent. He was full of information--the more general kind mixed with fun facts and trivia, and injected just the right amount of humor. He didn't "er" and "um" or add irrelevant personal information.
We had a most enjoyable time and heartily recommend the tour.