I recommend all leather for durability, and cleanability, should someone have an oops. My first leather interior is still in great shape after 27 years, my second is 9 years old and doing fine, and I'm just redoing the seats from their original vinyl of 1977 in nice leather this weekend on my third plane. The seats in my second plane (done in 2006, I bought in 2008) were done in FAR Part 25 fire compliant fabric, but they deteriorated rapidly in the sun, and were faded and badly wearing by 2009, so I redid them in leather then. They get stepped on every time you enter the plane, and splashed with water from time to time, and are in fine shape. I would never use any fabric on a seat again. The labour to do the work is the same irrespective of the material chosen, so by using quality leather, you can reduce the frequency of redoing the seats, and save money in the long run that way.
Consider having your upholsterer add extra pockets on the seat backs, now's the time! You can also replace the original foam with "memory foam" which is very comfortable. However, if you expect to sit on the seats when they are very cold, this is not so good, as that foam becomes very still in the extreme cold, and can break, rather than compress under your weight.