Galapagos land based itinerary question

Me and my wife are visiting Galapagos around Christmas this month and have 6 nights to spend there. Flying in to Baltra and flying out of San Cristobal.

We are not going to take a cruise and limit ourselves to land based tours to control costs and more importantly avoid sea sickness.

Given the time we have, we have two options, one is spend about 2 days each on Santa Cruz, Isabela and San Cristobal, the other option is to spend three days each on Santa Cruz and San Cristobal.

Would anyone be able to help me make a decision? We are not looking to dive at all, some amount of snorkeling, but mostly relax on the beach and most importantly see the wildlife. We prefer quiet locations and don't really need an active night life etc.

Given all that, would you advise us to do the three island itinerary or just stick to the two islands, I would like to skip the round trip boat ride to Isabela if possible, but can definitely do it, if it is worth it.

Thanks much in advance.

-S.