I have an old Compaq - which has a lot of little problems, but it refuses to die. I had an HP with a 17" screen which I really loved, but the hard drive crashed. I replaced it with a Gateway 17" running Windows 7 - it's OK, but it's got a few quirks.
I've never gone to Apple because I just don't want to learn anything new (at least anything to do with technology) so I'm still a PC guy, but I have a friend who just absolutely loves his Apple..
If you plan to switch, you should make sure that your broker's platform is compatible. Even in this day and age there are a few brokers that don't have a proper platform for Apple.