What bandwidth? What distance?
BT can be high bandwidth and is short distance. XBee is low bandwidth (56Kbs) and
longer distances 300ft outdoors, line of site, 1mW. If you buy a radio module
you will pay $20-$25 for either one. The trade-off is bandwidth and distance.
The Blue-Giga BT modules are easy to use. The XBees are trivial to setup and use.
If you think you want to talk to your phone then XBee is out.
(* jcl *)