My choice was 26"
I would have to agree with BillyK on all the points he mentioned. Plus, being able to fold it up and put it into a suitcase was NOT a concern of mine.
The bike trails I ride on locally are generally not in the best of repair, and so having the rear suspension and the larger tires makes negotiating the cracks and less than perfect surfaces a lot easier on this old body.
Far as the gear ratios that come with the 26" model, so far I am climbing all of the hills and inclines that I would normally need to climb, and as yet I don't remember actually needing to drop down into my lowest gear. Probably doing the steepest hills in 1 or 2 gears from "granny". And, I'm finding the Quest marches up these hills at least 2 or 3 miles per hour faster than I was doing them on my Catrike Expedition. Many folks, who have never been to Iowa much less ride a bicycle on our country roads, imagine this is pure flatland country. Believe me, it's not.... anyone who has ridden RAGBRAI knows that it is not flat. Yes, there are some areas that are pretty flat for several miles, but there are a lot of areas (carved out by an ancient glacier) that are quite hilly.
Having just come from a very low recumbent trike, I too enjoy the better visibility, not only that I have, but also being seen by other vehicles in traffic.
However, all that being said, I don't have an answer for your original question; as to which one is more popular. Maybe John Tolhurst will jump in here and give us some real numbers as to what has sold the best.