If you can the obvious choice would be the DVX100b, although I don't know what they're selling for.
I rented a DVX100 to try it out before I purchased my DVX100a, I didn't really know what I was doing and still managed to get a respectable test. When I got the DVX100a I was able to produce a much better image - a lot more filmic. However, I didn't have enough experience with the 100 so I would say that the difference might have been operator.
Unless their was a significant price difference I would go with the DVX100a.