Thats a loaded question. The best depends upon your skill with Linux, what you want to use it for, your preferred GUI, type of packaging system.... tons of factors
Being that you are just starting out and would like to experiment a bit I got two Distros you should try out and see which one best fits you.
First one is my personal Fav and what I use to teach friends and Collage students around here how to use Linux. It's called
PCLinuxOS. This distro is not only very easy on beginners, it also doesn't tie your hands behind your back, allowing for the full Linux experience. And when you run into something you don't understand the support on the PCLinuxOS forum is second to none. They are not full of themselves like some Linux geeks (even myself on occasion

) are.
Second one you should at least give a whirl is
ubuntu. Personally I find this distro a tad annoying to use, but I know alot of people that swear by it. It is geared to be user friendly to the extreme. A good starting point to become acquainted with Linux.
If you have any more questions you need only ask.
Oh, and let me leave you with some advice that really helped me when I started using Linux:
"With Linux it isn't so much the learning curve as it is the unlearning curve. You have to forget how you did things in windows and start fresh."