Here is an advice : stick to one Linux distribution only and buy a book (paper) about it. Once you are at ease with one distribution, you are easily able to understand the differences between the other ones, and select the one that better suits your needs.
Personnaly, I began with Mandrake with the book "System Linux", O'Reilly editions , then Debian, then Knoppix, then Ubuntu, and my quest has finaly ended with Pardus.






