3
Mostly splearn is infinitely easier to install. The language files are easier to fix and the interface is a bit cleaner and more logical. Functionally, they are quite similar.
Moodle on the otherhand is very cumbersome from an admin perspective and seems to have a great deal of difficulty in working with Xoops.
btw. I have also asked this question on the
http://spaghettilearning.com forums. Check it out if you et a chance.