Which to Power Up?

Go for best movesets.
That means Blizzard one & Zen Head one.

Blizzard Lapras only.

Ice Shard Blizzard, let Lapras be lapras

zenbutt is better for offense
while confusion better for defence gym.

Where's my Lapras!!! level 29 and 500k dust waiting...

Moveset is always more important, and they still have good IV. Like the rest said - Blizzard and ZH.
And you should power them up if you want, they are awesome to attack with

Definitely blizzard. I know it has lower IVs but the moveset is the more important aspect here. 78% is still very good. The other Lapras is also fine (after all it's a Lapras!) and it will do great vs dragonites but it's not worth investing dust which you could have invested in the other one.
As for the Exeggutors everything is said I think. Confusion is better on defense while ZH is better on offense. My personal opinion: power up the defensive one. I generally believe that defensive Pokémon should be prioritized with powering up. 1700 vs 2000 is not gonna make a huge difference when attacking (although of course it will be noticeable) , howeve, it will make a huge difference with regard of gym placement

Blizzard over Dragon Pulse for sure. Dragon Pulse is the weakest move on Lapras, similar to Earthquake on Snorlax. They aren't useless, they're just not as good as the other two moves, mainly due to lacking STAB.

Don't bother waiting for a better Lapras, for every person that does end up waiting and finding a better Lapras, there's probably 999 other people that don't. Even if you do find a better Lapras, the one that you have is still really strong, definitely still usable and worth powering.

As for the Exeggutor, depends on what you're using it for. On defence, confusion beats zen headbutt, but zen headbutt is close. On offence, zen headbutt beats confusion if you're spamming the move off cooldown.

If you're the type of player that dodges every quick move to maximise your damage before fainting, then it depends on the defending pokemon's moves.

for example a 1.5s move on defence means you can only fit in 1 quick move before dodging, so you'd rather have confusion because it deals a bit more damage.

however for a 2 second move, you can fit in 2 zen headbutts but still only 1 confusion, so in this case zen headbutt would deal more damage between dodges.

if you don't dodge, or only dodge charge moves, then go with zen headbutt.

and don't get worked up about IVs, especially on really rare pokemon like lapras. a ~10% difference might seem like a lot, but it's only 4-5 stat points, and pokemon near the top of tier lists have around 600 stat points total.

also IVs rarely make a difference in combat, because damage numbers are rounded.

I would recommend to go with Blizzard Lapras first. This is good defense set, but would work nicely as Dragonite butcher as well on attack.

I have split feelings about your Exeggutors, though. They both good, but on defense Exeggutor not very impressive with Solar beam, as it's easy to dodge, i prefer Psychic or Seed bomb, with Seed bomb more annoying. Kind of lowish CP puts Exxegutors on the very border of gym play in many areas.Which is a bit disappointing, as i have couple powered myself, but with every passing day gyms shift more to higher CP pokemons. With mostly Dragonites, followed by Snorlax and a whole army of Vaporeon\Gyarados. Not many Laprases in my area, I can see them eventually, but way less than Snorlax\Dragonite. So if you thinking about powering Exeggutor for gyms, than you better go with second Lapras first in fact.

I would probably power up Confusion\Solar Beam one eventually and then other one, but without any rush, only if not have anything better to work on, or if have not enough pokemons for gym placement.

Unfortunately in current state of game gyms are still kind of broken. Defense is really not working well even with best pokemon with best movesets. They still weak and average attacker can bring strongest gyms down solo with very little problem. That might change at some point, however.

I would not waste my stardust on these. Save your stardust, u will get better pokemon with better iv in the future, and u will be needing all the stardust by then. Trust me, these pokemons u have here is not worthy for powerup. What will u do with them if u have a 98% lapras next week? Save it. Gen 2 is coming out, u will need stardust then

Lapras with dragon Pulse.
Dont listen to people who says blizzard is better. They have never fight against several Lapras and only look at numbers on websites.

Dragonpulse is better at defending than Blizzard, by far, even without stab. Its tougher to dodge and comes more often. I dodge 100% blizzard with any pokemon.

PLus th DP one has a way better IV.

GO FOR THIS ONE.

Dont power the exeggutor. 1rst has bad moveset, 2nd has quite bad IV.

I'm glad, at least the last answer (Impala) was a well thought one, without looking on pure DPS. Yes, Blizzard is better for offense, but defensively Lapras sometimes fires out a Dragon Pulse twice in a row without an announcement at the second time, which makes it quite hard to avoid 100%. Blizzard lasts so long, that you can hit a Flamethrower at the beginning of the attack and would still be able to dodge. 89% is also simply great, since as a gym defender, due to Lapras now mediocre CP, every IV DOES matter imo. If you wanna go for a defensive Lapras, you absolutely should go for the Dragon Pulse one. It is identical to Ice Beam, just without Stab, while still having a great coverage.

It might be preference, but concerning the 2nd Eggy I would say go for it, if exeggcutes are harder for you to come by, because IV on an attackers mostly dont matter that much. You have 15 Attack IV, which is the most important stat anyway. If you are looking for another Eggy with that moveset, chances are 5/6, you will end up with a worse one.