It depends on how you want to work.
Bootcamp gives all of the machines resources to Windows, resulting in a high end experience. The downside is you have to boot into whichever environment you want to run, OS X or Windows.
Using VMWare Fusion, Paralells, or Virtualbox, you can run both OS's simultaneously. Because you are sharing reources, you should max out the RAM so that each OS has sufficient memmory to run well. Fusion and Paralells seem to leapfrog each other in performance with each release. I haven't used Virtualbox in awhile, but it was a bit harder to configure and slower than the others. Fusion and Paralells are built for just this purpose with lots of support, which is important for my business customers. For whatever reason, customers that ask for it seem to ask for Paralells more than Fusion.
Cost is another issue. After buying the Mac, you need to buy a licensed version of Win 7. Bootcamp is free. If you go the virtualization route, Virtualbox is free but you need to buy VMWare Fusion or Paralells.
Almost half the Macs we set up run Windows as well. As I said, mostly we have been using Paralells, but we have lots of Fusion installs as well.