If this is for DVD release and the choice was between the F900 and the Varicam, I'd go for whatever gave you the better rental deal and allowed you to use the high-end HD zooms and primes. The optics make a big difference.
If the rental was the same, I might favor the Varicam since 720P would be fine, resolution-wise, plus it's slightly smaller & lighter and does multiple frame rates.
One problem with the lower-end prosumer HD cameras is the small CCD's, giving you more depth of field. Plus the lack of good lenses, plus the compression and limited color depth, etc. Their main advantage is cost of purchase.