If you don't need transmit capability, the SDRplay RSP1A has phenomenal receive performance for the price. If you do need to generate signals (and you understand your legal obligations), the Red Pitaya, LimeSDR and bladeRF are worthy alternatives to the HackRF.
The Red Pitaya is a particularly compelling alternative from a hardware hacker's perspective, because it does double duty as an extremely versatile measurement and data acquisition device.
The Red Pitaya is a particularly compelling alternative from a hardware hacker's perspective, because it does double duty as an extremely versatile measurement and data acquisition device.