Which weapon should I pick?
ATM wielding:

awakening: PEN Dandelion jordun, Jetina's fully upgraded;

mainhand: TET Kzarka battleaxe, reform level IV;

offhand: TET Kutum shield, havent touched it yet, reform level 0;

Dont do grinding much, mostly lifeskill, not very active due to new job, no idea when and to what extent I could be able to divert my time to playing games.

Or should I choose none, then what instead? Maybe just claim then sell to CM?

Thanks in advance.

Are you playing mostly succession or Awakening? If Succession, use the mainhand Blackstar. You can give the tet kzarka to an alt for example. For awakening, get the awakening BS, and also give the pen dande to some alt.

Forgot to mention, everything is C0 atm.

When I do grind, which is rare, I grind in Awakening stance.

I'm sort of hesistate because if I choose Awa BS, my Jetina V becomes waste of so much time and resources, and I cannot undo all the reforms...

Thats just how it is sometimes. In the end, the blackstar is far more valuable than the Jetina weapon. And who knows, perhaps one day we can use these jetina weapons for something else (eg slumbering origin weapons)