I purchased Parallels without really knowing anything about it, needless to say it ended up being a waste of money and went the bootcamp route. It ran slow with parallels, for me it was really hard to run hard programs such as CS5 (which is what I needed). With bootcamp everything runs as if it were an actual windows computer. I think in the long run you will save a lot of time and frustration if you just use bootcamp.
What kind of programs? I've been very impressed with VMware Fusion 4 - but it's also all I know. I've never used bootcamp or Parallels. Which Mac do you have? That has to be a consideration as well.
CS5 and Microsoft Office will work fine in Fusion, however, Steam and Mass Effect 2 are another matter. I would go with running Windows natively from Boot Camp to make certain you can play the games you like. Only running Windows natively will give you the full power of 3D and graphics that you need when gaming.
It sounds like Bootcamp will be your best route with those type of programs. It honestly is annoying trying to run windows while on MAC mode. I find it simpler to just use windows as if it were a windows machine via bootcamp.
Even CS5 will be noticeably slower in anything but Bootcamp. Any time you start sharing hardware resources (as in virtual machines) you really cut your processing power. Other than Office, the apps you mention will not be worth using at all in a virtual machine.
I will highly recommend Bootcamp. It will take up no more room than the VM image you create in either Fusion or Parallels. It will be running natively on the hardware, the drivers are there already and it will not slow down the machine at all. It is just dual booting between OSX and Win7. Oh, and I only recommend Win 7.
I use my Bootcamp for Steam and Halflife (still love the game) as well as Rifts and CS3 and Vegas Pro (video editing). I have never had an issue and man, it is FAST.
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