Red Hat flavors or Ubuntu tend to be the best overall from ease of use, retention of power, and breadth of software.
I would do this if you are looking into going linux. Before even dual booting or going cold turkey, install VMWare player and grab a Virtual Appliance of Fedora 7 and Ubuntu 7.04 and play with each. This will give you a good taste of what is available while still being able to go back to Windows instantly to do anything that is confusing or impossible with your skillset under Linux.
I may add Linspire to the list when Linspire 6 is released and get to play with it. If Freespire 2 is any indication of what to expect, Linspire is fucked