There are loads of good lights out there these days. It all depends on your needs what brand you buy, and how much you can (or want to) spend. I have a lovely Lupine light - German made, superbly engineered - that is utterly reliable, casts a nice even light, is powerful and has never let me down after several years of frequent use. But it is also expensive. My daughter has a quite serviceable Cateye light that has done a winter if regular riding and also never failed - it cost much less, a bit over £100.
If you are riding regularly in dark roads, towpaths etc it will pay you to spend a bit more. Cheap lights, which often are unreliable and prone to overheating, can be a false economy.