Which Lapras to power up?

I prefer with 93% IV...

FB has a huge advantage vs IS and Dragon Pulse is also a good counter to DRAGONITE beside from Blizzard...

depends on the CP, although I wouldn't spend too much dust or candy powering up attacking Lapras (Frost Breath). The thing about Dragon Pulse is that it lacks STAB, and it's only single super effective into dragon types. So you're basically losing out on STAB bonus, and double super effective versus Ice Beam. I wouldn't bother with DP Lapras.

Defensive Lapras with IS / IB (or Blizzard) are worth powering up as high as you can afford, as they are all star defenders in the gym. In fact, the IS / Blizz combo (even with the IV% disadvantage) is going to be a far superior pokemon to the DP version in every scenario.

It depends on what you're after, and what their current cp is.

Ice Shard & Blizzard makes a very good defensive moveset. If you're after a defender I'd power that one up, but if you're looking for an attacker go with the Frost Breath one.

Having said that, neither is going to completely shabby used in either role.

What is the purpose for powering up? That should be the first question you should ask yourself before you power up anything.

1) What is the IV distribution for the 75% Ice Shard+Blizzard? Lapras has huge base Stm, so if its Atk and Def IVs are good and it just has wimpy Stm IV, then don't hesitate to power it up.

2) Are you wanting an attacker or a defender? ... Ice Shard+Blizzard is actually better than Frost Breath+Dragon Pulse for both.

Seems pretty obvious to me, if the CP difference isn't crazy, I think you should go with 75% in pretty much every case. Frost Breath / Dragon Pulse is a really bad moveset whereas Ice Shard / Blizzard is monster.

Ice sharrd/ Blizzard for me