Each distribution is a seporate product. If you focus on distributions not that they happen to use the Linux kernel, you'll be in a very good place to evaluate (given your exprest interest in experimenting).
Use liveCDs and/or virtual machines (Oracl Virtualbox is free to download and use).
Good places to start:
http://www.linux-chooser.com/http://www.tuxs.org/chooser/In terms of distributions, like the post above; it depends on what you want to do with it. A good general purpose distribution to start form seems to be Mint Linux though. Think of it as Ubuntu Linux with better hardware support and polish.
If you want eye-candy prety, maybe look at Elive Linux.
The usuals apply of course: Mandriva, Fedora, Ubuntu..
