[flakeoil]

Not OP, but Atmel AVR or TI's MSP430 are good choices if you need low power. The nRF24L01+ from Nordic Semiconductor is a good RF alternative for low power and long distance.

[ElectRabbit]

MSP430 are pretty much legacy (exception: the MSP430FR has its niche) since ST released the STM32U0.

[shakna]

AVRs can be serious power hogs, though. Not all have the Power Reduction Register.