It's quite difficult to tell... Some people like AOSP roms better, some Stock...
LG's stock is amongst the best of stock roms imho so I suggest you first get to know it and then figure out whether you'd like to change or not.
As for kernels, same story here: if you prefer stability, stock is always better. Battery life is not dramatically improved by any of the kernels I've tried and it's really a matter of preference...
Sorry buddy but these questions either lead to "the depends" answer or to a non-sense argument, usually between stock-partisans and AOSP-partisans... Although for LG there seem to be a consensus around stock being very good anyway, unlike some other brands.
Now for the personal taste: CloudyFlex 2.2 with CloudyKernel is my current daily driver. Stable and smooth plus some great features from Flex rom.
If I helped you, please thank me