The first question should be what do you want it for? Hiking, biking, working on a vehicle, etc. Use case/Beam type is a big deal because a flood beam will be great for close up work, for example working on a car, but horrible hiking/biking.
18650 lights are to me the sweet spot, good power, good runtime and not too heavy if you have to wear it for awhile. 21700 batteries get pretty "heavy", it's more that the headlight won't stay stable unless you crank the head straps down super tight, which give most people a headache. AAA lights while compact/small just don't last long enough at their stated runtimes.
Also beware of the manufacturers listed lumen/runtime rates, there's a lot of #'s manipulation going on. The FL1 spec says that a company can list whatever lumens their light can achieve after 30 seconds of being turned on, and then list the runtime until it's 10% of that initial brightness. The only way to find out what they are really doing is to see a runtime/output graph that most companies won't give you. What does all that gobbly gook mean? A company can make a light that is 3000 lumens for 60 seconds, and then steps down to 300 lumens for 5 hours and put on their packaging "3000 lumens with 5 hours runtime" when in reality it's a 3000 lumen light for a minute and a 300 lumen light for 5 hours. It's just something to be aware of to not get sucked into thinking that these lights really can put out that much light for the runtime they are listing.
I've used lots of them Olight, Fenix, Surefire, Zebralight, Milwaukee, Coast, Petzel, Light N Motion, Nightrider, Turbocat, the list goes on, most for biking/hiking and working on vehicles. Honestly one of my favorites recently is the Coast XPH30R, I like that you can adjust the beam from a super wide flood to a hot spot with good spill light and it's smooth/even at both settings, the switch interface is intuitive, 18650 batteries, it has good brightness and runtime, you can charge the battery in the light so you don't have to drag a charger with you, and it's $50. They have a larger/heavier unit out the XPH34R that uses 21700 batteries but to me it's too big/heavy to be stable with the strap. My other favorite that would be my choice for a "I abuse it" light is the Zebralight They also offer 3 options for beam patterns an 3 LED color temp options. I've used a few of the Olight and Fenix models and honestly haven't been that impressed with many of them. Olight I've never really had any problems with, but their lights just "feel" cheap to me, and I don't like the proprietary charging cords. I recently tried the Array from Olight and pretty much hated it. It has a combo spot/flood beams, but neither by itself is that bright, so unless you want both for say hiking, it's a waste of output. The Prerun looks okay, but for the price I'd rather just have a Zebralight. The one Fenix I used that I did like and still have is the HL60R, super beefy but pretty heavy.