My guess is the Smok xcube II is fine. They have been out awhile, so not as much online discussion as, say, the Smok H-Priv.
Samsung, LG, and Sony batteries are rated high for performance and safety. Different ratings for different purposes (e.g. higher storage or -mah vs. more power, can't have both). I'd expect Pansasonic to be good also, just not experienced with them. I usually get LG HG2, or Samsung 25R, as good all around batteries.
Not sure which tanks your folks are using with their mods. Some vapers feel the need to start with mouth to lung vaping, meaning doing a double inhale like when smoking analogs. This usually means more restrictive airflow, less clouds, higher ohms (often above 1, not sub-ohm), higher nicotine level, more throat hit.
Sub-ohm vapers generally like an airy draw, direct to lung inhale (not the double-drag), and bigger clouds. Usually this means a lower resistance (ohm) coil. The juice goes faster, and battery life is less. Also, with sub-ohm, there's much more vapor, so you don't need as high a nicotine level in the juice.
A mouth to lung tank might be like an Aspire Nautilus, run 1.8 or 1.2 ohm coils around 15w, drink juice and battery life slowly, offer a tight, restrictive inhale, often using a higher nicotine level juice, producing a throat hit but smaller clouds. Just a generalization, but an example.
A direct inhale tank could be a Smok tfv4, tfv8, Aspire cleito, a variety of Horizon arctic and Sense herakles tanks, and many many more. There's no right or wrong way, though most of the recent innovation has been on the sub-ohm side, whether tank, rta, rda, etc.
The Herakles tanks now have a wide variety of coils, so you could run an 0.2 ohm, 0.4 ohm, 0.6 ohm, 1.2 ohm, and 1.8 ohm all in the same tanks. So, you can get everything from decent flavor to good clouds, all from one tank. However, the tfv8 seems like the one to have if you want to run high wattages and chuck big clouds, using a tank with prebuilt coils (plus an option to build). For clouds, I stuck with the tfv4 because I don't really want to vape at such high power as many of the tfv8 coils like, and the tfv4 can still fog up a room in a hurry.
The Vaping 360 site probably explains these sorts of tradeoffs much better than I do. Worth spending a little time there.
