Hmmm, there are a number of differences between the two.
Minorating works by calculating each driver's safety rating and (in the future) making possible to refuse connections from driver's with bad ratings. This plugin will be installed on each server that wants to use such features but will offer no centralization other than (maybe) a global safety rating list.
raceme.io goes further. They'll have a number of servers, their own, and when you will start a session the raceme.io module will automatically connect you and other similarly-rated drivers to the same server. It's not a plugin for server admins, it will be a paid service and it tends to work "automagically".
For those who prefer to organize things their own way Minorating seems to be the obvious choice. For gamers who just want to go close-racing in MP raceme.io will be awesome.