For pure power (DNA-250C) - LiPo. 400W on a 4S pack? Can't beat it, really. Also, if running low power, you can run for a REAAAAAAAAAAAAAAAAAAAAAALLY long time. Issue is - charging it. It can take FOREVER. They also don't like being used and charged at the same time. Now you got me wondering... a 4S LiPo based mech. Wouldn't it just be a quad stacked mod?
"JESUS CHRIST JIM! THAT'S 14V OF POWER HITTING YOUR coils!"
For ease of use - 18XX0 (350, 450, 500, and 650), 2XX00 (20700 / 21700). batteries die? Swap em out. The issues arise when you need 2+ to power one device. batteries can get heavy you know. Guess it's time for some of us to invest in a battery case large enough to fill a duffel bag...