Was in a similar position not too long ago. Opted for Canon XF series for a few reasons:
1) 50mbps 4:2:2 recording. The EX stops at 35mbps 4:2:0 unless you buy an external recorder.
2) CF cards are more affordable and accessible than SxS cards. If you need five cards you're looking at a $4,500 savings for similar capacity, and a bonus is if you're shooting stills CF cards work in those cameras too. Don't try having a single card do double-duty.
3) It makes the BBC's list of "Cameras Approved for HD Programmes" which isn't exactly a long list. The EX cameras make that list, but you need to add an external recorder which boosts your total cost of ownership.
http://www.bbc.co.uk/commissioning/tv/production/delivery/hd-production-del...
4) It's Canon. We're familiar with Canon video cameras.
5) The LCD opens on both sides. If you're doing interviews this means you can finally be on the right side of the camera and see the shot.
Downside:
1) XF cameras are fairly new. This is good as it's new tech, but bad as compatibility and build quality are a bit unknown. They seem well built for the record.
2) I can confirm they work with CS5.5 and FCP7, but I'm not sure how universal they are. They shoot in XDCAM HD422, so they should be widely accepted, but being new it's hard to say.
3) The XF30x don't really seem to be able to snap-zoom. There's a ring/rocker switch to toggle between them, but it seems the motor is still driving the zoom mechanism. There are hard stops on the zoom ring and it's responsive, but there isn't a clutch giving you a direct linkage. There is a clutch to give you a direct linkage to the focus mechanism on the XF30x.
4) I found the EX1R to feel like a bit more serious camera to use than the XF300 and 305.
Personally I'd say it's a tossup between them. If you need snap-zooms the Canon isn't the way to go. If you need a lot of media cards the Sony's cost of ownership jumps pretty quickly. If you aren't going to get an external recorder the XF300 gets more detail. If you're going to be shooting in the dark the EX1R or EX3's larger sensor and 4:2:0 color space will produce less visible noise.
If you're able to get your hands on either camera (rental, loaner, etc) and play around with it the solution could become more apparent.