Part of the problem in sorting this out is that there are TWO very different issues that need to be considered: (1) The actual format differences betwen DV and Beta SP (2) The differences in typical camera quality between DV and Beta SP(posted 9295 days ago)As far as format difficulties, Beta SP is a more robust format and offers better image quality... the 5:1 compression in DV is impressive, but you're still more likely to run across jagged edges in DV material than Beta SP.
When you look at typical camera quality, there is a huge difference between Beta SP and DV. None of the good mini dv cameras (ie vx1000 and xl1) offer flexibility and features of your typical beta sp camera. The lack of rack-focus ability on both the vx1000 and xl1 is particularly frustrating when doing the types of shots that most people expect in a film. (Note: there are ways to get rack focus abilities with the XL1, the Cannon EOS lens adapter, an EOS lens, and a wide angle adapter.)
So, why go with DV? Well, because Beta SP is still darn expensive, and mini dv gives you some great images at a much lower price point (like a decimal place).
As for work with post houses, that shouldn't sway you. We have a non- linear editing system set up here (Digisuite LE and SpeedRazor) where we read in the DV or DVCAM tapes, edit on the system, then master out to Beta SP. It's not hard to find places that offer this option. Granted, there aren't many post houses that offer firewire transfer, meaning you may end up with an svhs/y-c interface and sacrifice a bit of quality, but more and more houses are getting either firewire ability (remember, firewire and dv are two totally seperate things) or getting dv decks that have good component in/out options.
Good luck! - John