I don't know many of us here that would identify either one of these cameras as our "weapon of choice" for shooting greenscreen.
The 1 or 3 CCDs is the least of your worries, the VX1000 is DV...4:1:1 color sampling and the JVC is HDV, 4:2:0...the tape format will be the most significant factor here.
The fact that you are buying either camera tells me you probably have experience with neither...that is also a decided disadvantage as the key to making a prosumer camcorder over achieve is to be very familiar with the camcorder so you can compensate for its shortcomings.
I guess I'd say give the JVC a shot as at least you'll have more real estate to work with...though either one of these cameras simply has too many "auto" functions for my personal comfort level.
You'll want to get as comfortable with whichever camera is your final choice before you are shooting for the job as that will be key to making it work.