The 40T will give you the most power, the 50e will last longer but not as powerfull.
I use the 40T in my l21a.
I think the 40T (assuming these are genuine Samsung cells) has a much higher amperage rating than the other two, allowing a high-current circuit to produce a bit more peak lumens. With a listed max current output of 8A for the light, I don’t think you would benefit much if at all from a 35A cell, though. So I’d think one of the other, higher-capacity cells would make you happier. However, that’s a guess on my part; others may chime in who know more.
Just want to say thanks for your tip on the Manker MC12 deal! I just ordered one for $34.95 from Manker USA. 
Before I read your post I almost bought it on aliexpress for $10 more, shipped from China. 
I’ve been wanting to try an NM1 light and I like the size/shape of this. I only hope I can live with the funky UI, too bad it doesn’t have the much better UI of the Manker U22 III (SBT90.2) another interesting model, but I didn’t see that one on Manker Light USA.