On XBee vs the 3DR Radio system (and it's clones), besides the big price difference. I've read comments elsewhere that the XBees are in some unspecified way more configurable and can implement encryption, but the cheaper 3DR clones have everything I'd need:
The 3DR Radio telemetry system is designed as an open source Xbee replacement radio set, offering a lower price, longer range and superior performance to Xbee radios. It's available in 915Mhz and 433Mhz; and in the following configurations: serial board (for the air) and USB (for the ground).
Hardware Features and Specifications:
Very small size
Light weight (under 4 grams without antenna)
Available in 915MHz or 433MHz variants
Receiver sensitivity to -121 dBm
Transmit power up to 20dBm (100mW)
Transparent serial link
Air data rates up to 250kbps
Range of approx 1 mile
MAVLink protocol framing and status reporting
Frequency hopping spread spectrum (FHSS)
Adaptive time division multiplexing (TDM)
Support for LBT and AFA
Configurable duty cycle
Built in error correcting code (can correct up to 25% data bit errors)
Demonstrated range of several kilometers with a small omni antenna
Can be used with a bi-directional amplifier for even more range
Open source firmware
AT commands for radio configuration
RT commands for remote radio configuration
Adaptive flow control when used with APM
Based on the HopeRF HM-TRP radio module, featuring an SiLabs Si1000 RF microcontroller
https://diydrones.com/profiles/blogs/announcing-the-3dr-radio-telemetry-system