It depends on what you need from a light, any from to be legal, be seen hopefully, or to see with. Its not just about how bright a light is but how useful the shape of the light is, and if it is robust, easy to change batteries, waterproof. Even how easy it is to put on and off your bike, or not switch on accidently in your bag. That doesn't mean it has to be expensive, there are quite a few recommendations for the Smart Superflash and the Mars Rear light, both of which won't break the bank.
Until last year I didn't think I could justify having the Hope 1 as I don't do that much riding in the dark, and its in a city, until part of my route changed to take in a very dark unlit section complete with potholes up to a foot across. Now I don't know how I ever lived without it.