I would highly recommend to stay at Christopher's Airbnb! The location is good, your quickly in the city center by public transport and also in the balboa park. Furthermore it's not.too far to Coronado and its beautiful beaches.
The room was even better than we expected, well equipped (with a fridge, microwave, a HUUUGE tv, dishes etc). And Christopher was an awesome host, we gave us advices what to do in San Diego and the general communication was very good. Also we allowed us to use his kitchen several times, so we were able to cook.
It was definitely one of the best Airbnb experiences I've made for two persons!