I have done both (although not a Cruiser): Kitfox S6 (IO-240) and a STOL 750 (O-200) from a kit (with friends). I have about 700 hours in the Fox and about 40 in the Zenith.
Each has its pros and cons. For me the Kitfox fits my mission better. It will not take off as short as the 750 but it will take off plenty short. The Fox will out climb and out cruise the 750 with our setup. I suspect other setups do better.
Visibility in both is excellent. Both are solid built aircraft. I would say the build from a kit is no more difficult for one or the other. Just different techniques.
I am in the camp of buy the whole thing. If the unthinkable happens and the company is no longer around it will be difficult to find your parts. I guess the 750 gets the edge here in that you get plans that would enable building from plans if you decided not to buy "kits".
I do not think you can go wrong with either. Get a ride in each. You will love whichever you choose. If you can get to Dublin, GA sometime we can likely get you a ride in each back to back.
I think the decision comes down to the mission. If you need to be able to take off as short as possible; Zenith it is.
As to the nose wheel decision on a STOL it was John McBean that told me the nose wheel Fox takes off shorter because it accelerates faster. Less wing drag, thrust line better, I guess? The STOL 750 is all about short take off. They also have a lot of room under the tail for rotation such that you can take off at ridiculous deck angles and let those slats work for you. That part is FUN, FUN, FUN.