Bluetooth is pairing-required and device-to-device (one sender-one receiver)
ANT+ is broadcast-receive, bunch of devices broadcast in 10m/30ft range with unique ID numbers, and bunch of devices within that range listen to a specific frequency and receive data. One ANT+ sensor can talk to many receivers at the same time, but with BT it has to be only one.

Also ANT+ should be more battery friendly since the communication is simple. It has shorter range than BT (and since the protocol is simple it is susceptible to interference) but on a bike it's perfect. (using turbo trainers with Zwift etc. usually BT is preferred though, or sometimes the ANT+ receiver is moved closer to the bike/trainer)