It depends a lot on your route. Some people ride in areas where the pavement is excellent and there is street lighting, so a 50 lumen flasher is enough because they just need it to get seen by drivers.

My route is on 60 MPH roads with 2 lanes and no shoulders, in pitch black through rural areas, and 4 miles of it is over gravel road with hills (25 MPH descents) and pothole minefields that pop up from one day to the next. I don't like to ride with less than 400 lumens or so, and I prefer about 800 when I'm in the rough patches.

My preferred light is the one sold on eBay currently labelled as a "2000 lumen bicycle light" - I would pick one with a smooth reflector, those are very spotty, then search for "magicshine lens" and buy that too. Both together are < $30. The lens widens out the spot so that you have a good pattern for covering the full lane of the road and simulates a cutoff to some extent so more light is going onto the road than into driver's eyes.

The "2000 lumen" lights are actually about 1000 lumens. Any of the cheap Chinese lights, figure they actually put out about half what they say. More major name brands typically give more realistic numbers, but you should be able to find a review that will tell you on those. The cheap Chinese lights are a moving target so any reviews aren't going to be of much use.

I don't mind the cheap lights at all. You do have to treat them with some care - the wires are not very heavy duty, for instance, so I've bought extension cords as accessories and used them as donors when the cord attached to the light fell apart, cutting one end off the extension cord and soldering it to the light. I only had to do that once. Now I use a short Y adapter and connect and disconnect that, so when it dies I just replace it, they're about $3. I have also had a charger die on me, and bought a replacement from Action LED Lights which is of much higher quality ($20). I have not had a light head die on me yet. I have had a battery seem to die but it was just full of water - most of the cheap lights aren't really waterproof. In that case I peeled off the plastic, dried it out, re-wrapped it with electrical tape and it's been back in service for a year.

If there's more budget, go to Action LED Lights and look around there. I would say go for Gemini, it's probably still a good brand, but they're now made in China like most everything else.