Everything has its pros and cons. In fact, I wouldnt DUMP Winxp quite yet. Linux ( as is true of Unix which it came from) is quite capable of 8 times the power on half the machine as Windows. Your ISP is probably using servers with less meory and cpu specs than your machine. If you havent experienced linux yet consider sticking on that old machine in the closet first.
As to Versions....
RedHat costs money. It has lots of toys for it. Its popular which is both a pro and a con since it means lots of answers AND lots of attacks. Since its really built around stealing the desktop business from MS its a good first choice. Its the easiest to install and get used to IMHO.
Debian is GNU and helps support the Open Source movement. If can be downloaded for free but I prefer to go ahead and order the CD's from gnu.org to make it easier. I figure if Im gonna pay Id rather help the cause than give it to a commercialized Version. Its horrible to install but its majorly easy to keep secure once its in. To be truthful I gave up and paid my local computer store to install it.
Those are the two linux Ive used. Ive also used BSD and Solaris (those are unix's). Here is a good site to go to for a comparison list.
http://www.distrowatch.com/dwres.php?resource=major