PTR vs BETA

Can someone explain to me the difference of what you can and can’t do on either?

the beta is like a demo the ptr is cut up of the demo
beta you can do anything that was put out on the beta
ptr has stuff cut out like new zones and stuff

PTR will definitely win because everyone has access to it.

PTR > BETA > ALPHA > PRE-ALPHA > FLOWCHARTS

Yes, this is a complete sentence, Blizzard.

Im basically trying to figure out which one i can test M+ on?

You can’t access the new zones, hero talents, or Earthen on the PTR. You can though check out Warbands.

You would need Beta Access to test M+.

PTR will only give you content available without the purchase of the expansion, so everyone can test it. You cannot level past 70 on the current PTR or access Khaz Algar, the new “continent” coming with TWW.

Beta allows you to test everything (well mostly) coming out with the expansion.

Beta is the complete content of the next expansion. You can hit the new max level, do the dungeons, all that fun stuff. Please don’t think of it as a demo because Devs are looking for your feedback and bug reports.

PTR (Public Test Realm) is an open realm that allows access to the next patch. You do not get the full Beta experience, such as leveling, the new zones, and what not. Mostly you’re going to be testing out the pre-patch content that’s about it. Again, the Devs are looking for feedback but in a wider scope.

With both forms of testing, NOTHING transfers to your main account except your knowledge and memories.

PTR is to test the upcoming patch, whatever it is.
In this case, it’s coming next Tuesday already, so it is kinda useless to go in there and test now.

Beta is to test everything a new expansion has to offer: new talents, new race, delves, questing, leveling experience, zones, raids etc.

Neither is exactly a preview, but they are primarily a testing environment to report bugs and test gameplay changes.