IMHO, the most popular probably would be the 500 series, of different variations, more available in the used market. I myself use a 503CW, with the add-ons.
The 2000 series have a focal plane shutter, while the 500 have a leaf shutter. One will need some ND filters with the 500 series
More info here, author implicitly (in my opinion at least) does not recommend 2000 series, but the 200 instead :
http://www.photoethnography.com/ClassicCameras/index-frameset.html?Hasselblad200.html~mainFrame
Money-wise, it doesn't make sense to go into film, if one shoots a lot (some will argue against that, but this is my experience).
I belong to the camp that believes film has a quality that is still unique and not matched by digital no matter how much it is pp'ed - again, more arguments will be raised against that but no time for that, it is my opinion and experience. Hence, my main reason to use a lot of film, not because I like the work involved or that I like the anticipation of waiting to see the results.
However, it's still just another medium, and I use it in conjunction with a dslr too. Even a Holga, pinhole or some archaic cameras have their uses, particularly for artistic stuff. Artistic low-resolution like those from one of my favorite photographers, her work is great (to me) =>
http://www.flickr.com/photos/kristmas_klousch/. And to quote her :
"although I really appreciate the feedback I have received I am more content to do my own thing and not worry if my images are popular according to anyones standards but my own --"
wise words ...