Depends on your budget. Based on the gun and use case, i'll assume you don't want to spend almost the same amount on the light as you did on the gun. Streamlight is super solid for a very friendly price. I haven't tried any of the Sig lights so I won't speak on those.
I've owned enough weapon mount Olights to never buy one again. Olight makes cool handhelds but their weapon mount lights are poorly designed, and i'm almost positive they've never tested them on an actual firearm. I've got 3-4 Olights sitting on my desk right now that I will never ever mount to another weapon. All that money spent and I could have bought a really nice one or two from Streamlight, and a super nice one from any of the companies below.
If you want high end - Surefire, Modlite, Cloud Defensive, Arisaka - not in any specific order.
Just my 2 cents.