You can scroll through the pages on the Vidanta website to see the differences. Here's the link to the
Rooms & Suites portion for the Grand Luxxe in NV. The other ones are simple to find by poking around on the web site.
You can exchange into Grand Luxxe, Grand Bliss, Grand Mayan, Bliss, and Mayan Palace through either II or RCI. Not all levels exist in all of the locations. You can exchange into the Grand Luxxe Residence levels through either the platinum level in RCI (so long as you are not considered a second or third class individual by Vidanta for having been silly enough to have purchased at any level with them) or through ThirdHome (same limitation applies, though you can exchange into a level equal to or lower than what you own. Nice incentive system guys!).
There are some additional differences in what portions of the resort complex (e.g., pools and beach areas) that you can use based on where you are staying. That is to say that if you are in Grand Luxxe you can use the Grand Luxxe pools and any lower tier ones - the tiers are in the order I listed in the prior paragraph.