My comments based on a superficial look at these three plans:
The three smallest are available on both an E350 and E450 chassis. I would definitely try to get the heavier duty chassis, as you'll have more weight carrying capacity free and not have to worry about overloading things as much. I think the whee track on the E450 is also wider, which should translate into somewhat more stability on the highway.
The two without slides will typically be somewhat lighter (slides add weight) and take slightly less effort to set up and break camp. I'm not a huge fan of slides generally, but many people do like them a lot. They have one advantage (more space inside) and a number of disadvantages; but that one advantage can be a very big advantage in some circumstances and for some people, it must be said.
The 26A looks to be the only one with any hint of kitchen counter space. If you like to do much cooking that is a definite advantage (even though it's still not very much counter space).
I would suggest looking at them in person if at all possible. The floorplans often don't show things that make a noticeable difference in actual use--things like how accessible stuff is with the slides in, whether there's a good place to stick the trash can, how likely one is to trip over the step up (if there is one)....