Which Blissey would you powerup?

Depends on the IV distribution, and your goal.

Want high CP? Go for highest Att IV.
Want maximum tankiness? Go for highest Def IV.
Stam IV won't have a big impact on Blissey.

Based on movesets, it seems like the general consensus is that the quick moves are more or less the same, DG is the best charge move, HB is also quite good, and Psy is suboptimal. But it also depends on whether you think Blissey's damage output or her tankiness is what's important.

The IV % doesn't tell the whole story, and for Blissey it is very noticeable (and Alakazam too...but in reverse).
You really want a full IV breakdown to make the optimal decision.

I would choose 2 or 3.

I dont know how much difference hyper beam and dazzling gleam have in dmg output.

I think enemy would want to dodge hyper beam, so they maybe more careful with it and stop attacking and you get few seconds off the clock each time chansey fires up hyper beam or they get hit very hard.

hyper beam gets stab and also 1 headbutt........because 2x dazzling gleam takes 2x more time than 1 hyper beam

Ask someone to calculate cycle damage for your movesets first. It looks like similar IVs and level, so your decision should be based on moveset.

I think (means: do not know) ZH / HB is the best.

I would say powerup that P/DG, since the IVs ( thus the CP ) will not be that far from ur best IV one.

DG is the killer defensive move for Blissey. Deals SE dmg to dragonites, machamps, tyranitars, and it slows down ur opponents coz they had to dodge more often for the DG.

In any case, check out this vid on ZH/DG vs P/HB ( https://youtu.be/v3EtoQuksp4 ). Arguably, P/DG could be better than even ZH/DG coz Pound can charged up DG faster.

Is that Att/Def/Stam?