Which Kyogre to max out.

Personally I lean towards the highest potential for stardust/candy savings, which in this case would point at your L31 with 15a. Between the importance of defense IV vs HP IV it's largely unnoticeable. You'd have to pour over particular raid bosses with a particular moveset and compare bulkpoints.

I'll say I'd go with the L31 Kyogre, but expect a lot of people telling you to wait now that the precedent of TM-locked legendaries exists. There's room for Origin Pulse to be limited to a 3-hour P2W window, at which point all of those resources spent here could be spent there. Granted, if you're not concerned about that type of thing then by all means go ahead, Hydro Pump Kyogre still decimates anything you throw it against.

The level 31, or wait on all of them long enough to see one turn lucky with a future update to lucky Pokemon that doesn't require trading, lol.

Wait until you really really need one or they have a special kyogre with precipice blades raiding day. But other then that the cp formula is reasonsble in that it prioritizes A overs H over D. Just go with the one with highedt cp at 40

Well it all depends on if you need a kyogre, if you dont, then theres no real reason to power one up. if you're concern is saving for origin pulse, then just use some maxed out gyarados, even if kyogre gets origin pulse, all those gyarados will still be good because their mega's a water/dark type, so they can easily become bite crunch sets. (even now, bite crunch can still really dent mewtwo)

All in all, if you're tight on RC, or want to save for origin pulse, use a gyarados, it isnt as powerful as kyogre, but its candy is more available, and had more potential uses if/when megas/primals are added and origin pulse is as well