it's hard to say which one is the best since everybody has a different preference..
but i would say that the logitech and microsoft ones seem to be the best.. best thing to do is go to a local computer store and try them out.. each one has a different feel to the setup and the way the keys feel...
one thing to note about the logitech keyboards.. watch out for the f-lock key. it can get very annoying since whenever you boot up your computer, it'll be off my default... this means that you need to enable it everytime that you want to use the F keys after a bootup...