JasonWW's points are worth considering too Tendou. In essence it all comes down to how do you intend to use your flashlight, be it in long continuous runs at some mid power level or mostly short bursts on high, and namely how will you manage its battery. I don't recharge often and also don't fully charge my batteries, I focus on cell lifespan versus having cells full or near fully charged at all times. With this in mind the 50E would make more sense for me.
Another thing to consider is how the flashlight driver works. Boost drivers, for example, make use of most of a cell's capacity and energy without tapering down output power and thus it all comes down to selecting the highest capacity cell which meets the torch's current demands without problems.
These cells just keep getting better and better. As most enthusiasts are already aware, version 3 of the INR21700-40T is in circulation from several resellers and are rated for greater charge cycles than its previous versions. This is one tough cell.
The cheapest genuine cells I could find from a US supplier is at Aloft Hobbies, and Ive purchesed several from them. While their stock photo does not reflect current stock, I just received a qty of 20 that are v3.
It’s basically a high amperage 3 volt LED. It can easily take 20 plus amps.
The best battery for that light will depend on how you want to use it. If you only use it a few seconds at a time and you want the absolute highest output (on Turbo), then you want to use a very high drain battery. It will pull the highest amps, but get hot very quick.
If you don’t really care about getting max output (on Turbo) and instead want it to run a little bit longer before getting hot, you can use a much lower drain battery. It will pull lesser amps.
This Samsung 40T is a nice middle ground battery.
The 30T will pull more amps.
The 50E will pull less amps.