nrf24l01+, enhanced shockburst with two "masters"
The second option is actually very common. Essentially, the PRX and PTX can be on a per-transmission basis. Both of them should be in rx mode most of the time, and when you need to transmit something you would first look at the status bit which tells you whether or not there is a signal present on your channel. If there is not, you set the send address and set your ack address and fire away. If there is, go back to rx mode and have some timeout period.

Your first option seems like your describing a beaconing network protocol. Like you observed, this has the downside of continuous traffic and more power usage. However, it is really the only way you can guarantee communication if anything is time sensitive.