Istick 50 W and MVP3 Pro. Both mods have the biggest battery at the moment.
MVP3 Pro has a better circuit which is more efficient, which translates in a marginally longer runtime, especially above 30 Watts.
Please note that battery efficiency decreases in a non-linear fashion as the current increases. While a very good Li-Mn or a Li-Po 18650 can provide 60 W to the load, the non-linear derating starts above 25 W.
Also consider that advances in the battery sector are just a trickle. Specific energy of lithium vape batteries hasn't increased at all - since the first mod hit the market.
As final hearthening note, consider that car batteries have trebled their capacity - since the first car fitted with a starter engine, a bit less than a century ago.