You get a surefire-compatible 9P body, this can be a Leef battery tube (best) or Elzetta host (2nd best) or something similar either specially built or bored to accept 18xxx Li-Ion rechargeable batteries.
You can then use a head compatible with 1xAA, 2xAA, 1x18650, 2x18500, 1x123A (or 2x or 3x) primaries with appropriate sleeves and/or spacers.
You can use a high-amperage tail cap. And with o-rings and a sealed head this flashlight can be pretty resistant against water. Also with a potted head it can be pretty resistant to falls, drops, hits,..., practically anything.
So. LED's evolve for the better, you can use a new drop-in. You can get 3xLEDs with power to put out thousands of lumens. Or Overready's M2 head for throw (or Malkoff's hound dog). Or you can use a nice M90 drop-in from Malkoff with 700+ lumens and great room lighting capability at reasonable run-times.
Or you can use an old M60 (or M60L, or M60LL) for insane battery compatibility, great runtimes, and excellent throw.
Or, you can use UV, IR, colored (red, blue, green,...), drop-in.
Or you can use a multi-level drop-in (Malkoff's M361 is great), so you can use one flashlight for low, mid and high level light.
Or...not sure there is something reasonable you cannot do, I mean even the monster surefire flashlights (at least the ones not designed to be carried by vehicles) have a few thousand lumens output which is within your reach.
So, what is it that you want to do that you cannot with this system! I think this is a pretty good definition of "best".