Without know what you want to do and how much you are willing to pay, there is no such thing as "best". And then, you will get a different answer from different people. In my opinion, for HF, AirSpy HF+ Discovery is the clear winner. For VHF/UHF, AirSpy II is the the winner (though I also own various others including various SDRPl;ay models). If you want only one SDR and are willing to sacrifice a little on performance, I would buy an SDRPlay RSPdx . If you want an SDR that is better for analysis (but will be much less good as a receiver), then get a HackRF 1. If the above (all above $100) are too expensive, save your money till you can get one of them--but if you cannot, get an RTL-SDR but you will really not have anything in the best category (however it will better than nothing).
