I converted to Macs two years + ago and have never regretted it. I have an iMac and MacBook
Mac OS X - current version is Leopard, is a joy to use. You currently do not need AV or Anti Spyware.
It will take you a while to get used to the differences but persist and you will not regret your decision.
If still you want to run Windows, (mainly if you play games) on the Mac you can. Either as a second bootable partition through an Apple system called Bootcamp. Or, as I do, by using Parallels or Fusion Virtual environments.
Which Mac Laptop.?
The choice really comes down to how much you have to spend. I have a MacBook (13" screen) which I really enjoy, however the MacBook Pro comes as 15" and 17" but of course costs quite a bit more. The MacBook Air whilst being a joy to look at is pretty under speced and expensive.
It is strongly rumoured that the MacBook will be updated in the 3rd quarter and will have an aluminium case like the MacBook Pro and MacBook Air. You may want to wait a couple of months if the MacBook is your preferred choice.