Size, price, features....
When selecting a white light or tactical flashlight, you must consider a few other features too;
Will you use it often or for extended periods? Then a rechargeable format may do best. Do you plan to deploy it with a sidearm or handle weapons with it? Then designs with tailcap lights or models that work with different methods like the Rodgers or FBI or Massad Ayoob may be needed. Do you want strobes, beacons or red/blue lights for traffic enforcement or tactical use?
Some models have anti-roll designs if you drop it & a few have edges to use as a defense weapon in a CQB event.
New LED & CREE styles are now brighter & brighter. Pick wisely and learn the best methods to deploy a white light when needed.