While I think they both have their merits, I lean towards the 3 wheel version. Just for the reviews on ease of moving them. I think they have a lot of good stability features while easier to push. I have not purchased one, but I've looked a few times and I'm always drawn back to the 3 wheel version. Though I don't think there is really a wrong answer depending on what your primary needs are.
I have never used a 4 wheel version, but of the 3 wheel ones I prefer the fixed front wheel - maybe it is becuase it is what I am used to, but I just found the swivel front wheel version took more effort sometimes to keep it going in the direction I wanted
I purchased one of first 3 wheel Clic Gears when they first came out. Never looked back after that purchase. It has pneumatic tires, but the front wheel doesn't swivel, ehich is not an issue at all. All I've had to do was replace the tires after about 10 years of constant use.
I know guys who have 4 Wheelers, and tbey are quite pleased with them. They also don't take up much room when folded up.
I think it just boils down to the individual's choice of what they want.