I have old old plaster (on lath) bordering new drywall. Is it better to use mesh tape or just paper?
Mesh is definitively a better blending product. I like to embed mesh with the lightweight setting joint compound and then use general purpose (premixed) joint compound for topcoat and blending.
AFA plaster cracking, there are large size mesh rolls meant for skimcoating and repairing plaster. One I know of is 36" by 150' by FibaTape