I've used Knoppix (versions 3.5x), SUSE 9.1 Personal, & I'm going to install Mandrake 10 as soon as I can reformat my computer.
I really love Knoppix, because if you do like it, you can just install it onto the HD, and dual boot (there's more info at
http://www.knoppix.org I believe the website is).
SUSE 9.1 Personal is pretty good, I like it atleast. What I like about it is that it's actually fast on my 500 MHz Intel Celeron 2 year old HP computer w/ 64 MB of available RAM (oh...my...gosh...I don't know I remember that all).
I'd say go with Knoppix, but SUSE also has a LiveCD version if you want to try that out. It's got a pretty good speed, and it comes w/ a graphical boot loader & also comes with GRUB.