Hypothetical Question

Although you have titled this as hypothetical, very similar situations have happened to me over the months of playing this game.
In the past, I spent candy and stardust as soon as it was available.

Now, I'm waiting and waiting.
For what you say?
I will not power up a mon unless I can power it up to the level I'm aiming for.
example:
I have 175 larvitar candy and a 89iv larvitar....
and an empty pokedex for pulp and t-tar.
But I'm waiting.....and waiting.... until I get enough candy to evolve and power up to at least 33 or so.

so to answer your question, Wait until you have enough for a full power up because a better mon may just come along.

added edit: oops if this is really about HB vs HS....
then I don't know, I don't attack with lax, only defend.

Would invest on ZH/HB already powered up one.
Isn't HB considered > than HS even in defense?

The HB one. While many of us that play more seriously easily evade HB you would not believe how many other folks fighting gyms don't or do it wrong. Also, HS isn't that great. While it may be used more I'm not getting hit with that either. And you aren't clearing Snorlax without HB coming unless he's very weak.

I would keep investing in the first one with HB until it got to a level you like. You may hatch a higher IV HS in the meantime.

Finish off your first project then plan a second Snorlax. But wait until you have enough candies before spending it on the 82% IV one. You may get a better one.

I have an 89% one I will eventually power up with ZH/HS but I'm saving candies until it can be 2800CP+ (preferably 3000CP) so it would at least be useful in gyms. No sense in having a 2300CP Snorlax with nothing to do.

C. Save your candies.

Are you kidding?

Hyper Beam simply annoys the attacker by putting the attacker into the dodge bug loop, and it tempts the attacker to really dodge.

Heavy Slam, although it comes frequently, outputs less damage.

Thanks for this question. I have an 89% zh/hb Snorlax that I have been holding off on. I invested in him a while back, but focused on my bs Snorlax when that became legacy. I have around 120 Snorlax candies now, but haven't decided if I should use them on that guy, or wait for a zh/hs one. At this point, it might just be best to wait for the gym rework and see if there are moveset changes.