my first zero image was the 6 by 6, and I've loved it ever since -- very basic, does lovely work. I got crazy and bought the 35mm one and it's not as sharp because it uses the same pinhole and film distance as the 6 by 6 one-- interestingly, using 400 film in it I've even, by bracing the camera slightly and using the cable adaptor, managed to do occasional handheld with it and done OK.
I recently got wild and crazy and bought their 4 by 5 -- the 75b system. It's lovely, and opens new vistas and is even slightly cheaper than the Ilford Titan and has 3 separate distances, with three pinholes so you're always shooting in the f-138 region, and it has zone plates I'm anxious to try out.
So I'd say, for a beginner, the Zero 2000 in 6 by 6 would be your best bet. That and a small tripod and some 100 film so you don't have to try to time short exposures outdoors, you're on your way. If you go through the galleries at the Zero Image web site you will see many, many wonderful shots taken with that camera.