I did the trip a few years ago with Galapagos Travel
Galapagos Natural History & Photography Tours | GALAPAGOS TRAVEL I chose them because of the extra time and attention to it being a learning experience. On our 16 tourists ship we had not just the local guide which all tours have, but additionally a university biologist from Washington. Each day we seemed to be the first group on the islands. We were in the water snorkeling with seals and one day with hammerhead sharks! (not too close). Each day we did at least 2 island walks and one water experience. Additionally we had every evening a one hour long lecture or talk if you like on topics of interest. I recall ones on tectonic plates, volcanism, Darwin, reptiles, of course birds, etc. The talks were neither too simple nor too complex. Keep in mind the Islands and the wildlife is the same no matter what tour company you use. You will only do this once and need to decide if you want to maximize the seeing and doing or is having lots of rest time and fancy meals a priority. I don't know how the price compares with other companies and of course who the guide is on your ship will be really important. I did really like having two guides for 16 rather than the usual one.
edit, one other thought. Some (?most) make you spend a day or two on the mainland. Be sure you look not at total trip time, but rather time in the Islands. Time of year also will change which species are most likely seen.