here is a detailed, however maybe a bit outdated list about the differences:
http://allods.my.com/forum/index.php?pag…d&threadID=7017
main diference is that free server = pay what you want and the other is pay a fixed amount
free server has more items, paymentserver has less and those who exist has everyone, so there is less option to become totally superior -> more "balance" and "equality" for those who like this
free server has significantly more players; paymentserver is a ghosttown according to many players
you can see yourself, when you make a new account you automatically have a few free days