Hi there,
For my final year engineering project im developing an environmental sensor network andXbee appears to be just what I need since I want to use an RF mesh. However Xbee 2 or Xbee 3? Im going to be using an arduino micrcontroller in each node to take sensor inputs as even though Xbee 3 can receive and process the inputs, this is because each node will have an SD card to save readings to. Im also looking at what is easier to setup to get the mesh working (limited time in the semester and studying part time) Xbee 3 can use Digimesh which i understand is more straightforward to configure the mesh with rather than Zigbee mesh.
I would go with the XBee 3 product. It is the newest product of the two and uses the most current stacks.
Really the difference in Digi Mesh to Zigbee mesh is that Zigbee uses a Coordinator to establish the network where by Digi mesh just needs nodes to be in range of each other.