Best solution for Mesh network? XBee?
I personally use Dust SmartMesh IP from Linear, and it is intended for mesh networks. There is a single manager for the network which you can use to centralize your data, and can even handle 6LOWPAN packets(you will still need to provide WiFi access as the stack has differences). The range is 100 meters indoors for each MOTE but can handle up to 300 meters outdoors. Has very good reliability and one of the best power consumption that I am aware of during transmission. 

Word of caution the transceiver shares the same spectrum space as Wifi, although it does have 15 channels and actively keeps track of channel integrity, it may cause problems in dense WiFi areas, I have personally not needed to worry about this thou.