I might lean towards KR808D-1 mega/XL batteries, with maybe an 808batt-510atty adapter if you really want 510 compatibility. The 808 batteries are higher mAH than the 510 standard batteries, let you run lower ohm cartos, and provide a higher output voltage (which equates directly to a bit more power/warmth). There are also a LOT of KR808D-1 prefilled cartos, if that is a consideration.
(A standard 510 battery is 180 mAh. A standard 808 battery is 280 mAH, the same as an XL/mega 510 battery. A mega/XL battery is 380 mAH. All standard 510 batteries are nominal 3.3V, vs. KR808D-1 3.7 - 3.8V. The mAH relates to run time and how low a resistance is considered okay to use, hjigher mAh means lower resistance is okay. The V is related to output power for a given resistance, bigger is more power.)
The above is based on the norms, however PV makers do keep twiddling with parameters, so maybe they are now making higher V and higher mAh 510s.