1.
http://freedomlives.com/ps2_version_identification.htm
2. All of the big name chips are compatible with all versions.
3. Messiah 2(
www.messiah2.com ), DMS3(
www.dms3.com ), and Apple Pro(
www.apple-chip.com ) are the top dogs.
4. If you have a v1-v4 use -r. If you have a v5 or higher it doesn't really matter. Ritek is a great brand to go with (available online only)
5. Older online games you won't have a problem with, but the newer releases now have a protection that doesn't allow you to go online with a backup. A way around this is being worked on.
Don't mod your v1. You will just run into problems with your laser, as v1-v3 lasers sucked. v4 are so so. v5 and up are best.