Tough decision, D21 vs. F35, makes me think, both look very attractive!
another show to check out is Human target, shot on D21, and ... Panasonic GH1, can easily spot which is which..
some read http://www.eoshd.com/content/tag/arri-d21
If it was me making the decision I would first choose the one that best fits my needs. If I was shooting weddings for example, I would never go for either.
If what I wanted is to shoot features, I would then check which one would be a better fit to the rest of my equipment. The D21 will need considerably bigger support and grip gear than a F35+Hyperdeck Shuttle. Shooting with a D21, even if you would waste it's potential and record to a Hyperdeck Shuttle, would be not much different than shooting with a 35mm film camera.
Then after that I would choose the image I liked the best.