But they are performing different roles.
FLARM is designed with glider collision avoidance in mind. It has a short range but includes parameters to aid collision detection.
ADS-B over 1090 is designed for ATM applications, and has a much greater power/range than the others, as it operates on a protected aviation band.
PilotAware is by far the lowest cost system, which has strongly supported its adoption (which is, after all, key to winning any standards battle).