Red or Alexa
So! The big question.
Well, the first big issue you'll have is getting hold of an Alexa if you want to shoot on one.
Certainly, if you can source one, the camera has that Arri stamp, which is worth its weight in gold. One criticism I've had of Red is the beta nature and forum committee involved, it was a revolution, but some of the people spearheading it were not film-makers, but rather geeks or pro-sumers who didn't even know what a prime lense was.
At least with the Arri Alexa, there is the support network, I've experienced it first hand this week as I've been speaking directly with the Arri guys here in the UK - something which would be near on impossible for me with regards to the Red guys, despite them being very nice when I have met them.
Either way, the Red gives great images, and the new Mysterium X chip delivers great images - and it has slow-mo (not available on Arri Alexa unless you're shooting on HDcamSR at present).
Workflow wise, if you're cutting on Alexa, the Pro-res files from the SxS will go straight in to your FCP (not with Red), if you're on Avid, the Alexa and Red are much the same as the material really needs to be transcoded to make editing easy (too slow otherwise in my opinion).
From my point of view, both come in about the same speed in to my system for the grade so I dont care.
Picture wise, the Red gives a clean, digital stills like image - it can be so lifelike and impressive its almost like being there. With the Arri, the image seems move filmic to me, more in tune with 35mm roll-offs and feels more natural to the eye for cinematic viewing.
The Alexa can currently shoot in two ways, Log-C (filmic roll-offs and very low contrast image) or REC 709 (standard high contrast video image). The former is preferred by most DPs as it can be manipulated into a more filmic look and should give greater latitude for the grade, the latter is easier for offline as the colour and black/white points are already normal, so no grading in the Avid/FCP which is without question a pain for editorial. The DP will need to test both, and decide, with production, which seems to be the best for the project. For my mind, I like the Log-C approach as I feel its gives me a little more control, but the difference isn't as great as one might think.........
Either way, both cameras are good, so its down to the DP to make the call - and of course THE BUDGET!!!