Best HD Camera for 4:3 NTSC Protection

Anybody have an opinion (backed up by experience/science, preferably not passion) on what is the best HD field camera to use if you know that the end user (a cable network, btw) will be using the footage full-frame 4:3 NTSC. (Shooting 24p over 60i)

I have had issues in the past with soft 4:3 downconverts, though I suspect the equipment they do the conversion on makes a difference as well.

All conversions equal, what's the better camera, the Sony F900 or F900R, Panasonic Varicam or HDX900...?

(And second logical question would be: If you absolutely know that the footage will ONLY be used in NTSC SD, is there any benefit to shooting in a HD format?)

Much appreciated...