To be honest with you, the best distribution is the one that meets your needs.
WAY back in 2001 there were not many solutions easily tried out - someone suggested using VMWare and that is a good approach now, but back then, that would have chewed up most hardware.
Around 2003 the notion of Live CDs really began to accelerate. Again, like virtualization, VMWare and other alternatives, the technology existed but the hardware was too weak. These days, burning a CD or a DVD and trying out a system live without ever having to do anything else or write anything on your current system is definitely THE way to go. If you ALREADY have a virtualization solution, such as VMWare or any of the other alternatives, then go with that, but if you do not have such a thing in place, then learning how to set that up is just as complicated, perhaps more so, than just burning an image and trying out a system live.
Once you start EVALUATING many distributions or you want the flexibility of running more than one system, a virtual machine (which is what people call "virtualization" today, is a great option. But I think it can be complicated. A newbie would not know anything about such an approach, and that is why I suggest Live CDs. Virtual Machines are for LATER in the game when you have some idea what you are doing!
Today Ubuntu makes a great option for trying out the software. It is NOT, by ANY means the only choice, but it IS a good choice. Fedora, openSUSE, Mandriva, Linspire, Xandros are just a few of the other good choices. Pick one that suits your needs or just start trying them out until you are able to articulate what you are really looking for, then hone your request into "What is a suitable system for doing specifically ... and name the features you want most. Again, many systems could probably do the job, but sometimes a particular feature is well handled by certain systems. The more specific you can be, the more likely you will be able to find what you are really looking for, even if you yourself do not know what that is - YET. Figure it out and you are on your way.