Which Larvitar/Pupitar to evolve?

pupitar I would think is the better option unless you can get a ttar from a raid. I am personally trying to get a couple extra ones with bite in case it becomes legacy

Close call, maybe wait a little longer and see how the buddy walking goes over the next 7 days. A level 20 Tyranitar 2070cp isn't a high performer, anyway. Either way it is a project. Maybe you get another 10k egg in that pondering time***However, if you don't have access to tier 4 and tier 5 and tier EX, now might be the time to maximize what you almost have

Do the one with the 15 attack if you are focused on the long term. That one point of extra attack IV is worth the extra 25 candy IMO. Remember, it's actually a little less than 25 different because you will hit break points one half level sooner. I would only do the weaker one if you are just desperate for a TTar right now.

Like you, I can't get Tyranitar from raids. I would go with the 96% 15A Larvitar.

Let us know what you decide to do :-)

Tyranitar is one of the few pokemon who will stay top in it's role for a very long time.
If i remenber right, from it's debut in gen2 until gen7.
He's a save investment, i'd walk him as long as i have to.
Graz btw, nice pokemon.

Is the Pupitar level 20 also? If it is significantly higher, then that might add a lot more weight to one side of the question.

I would evolve now. The reason is that bite might become legacy soon before you get your extra 25 candies and the difference between them is negligible.
You can try to speed up the process by placing the larvitar in gyms and feeding him.

If you think about the big picture, you'll probably end up powering up both, unless you get a lot of better Tyranitars/Larvitars. So the downside to powering up the Larvitar is that you need to get another 25 candy, which is 12 days of walking (once you factor in the one you get from the evolve.) I'd do the big one, and once it's powered up, then pick the next best one you have to power up.

But, as was said, be cautious because gen3 might give us a moveset change (which could be better or worse); if it gets worse, you'd want to lock in a good moveset now.

Maybe the best answer for you is to look into a raid group that operates near you (or near enough), and try to do a few Ttar raids. Not only do you maybe get a Ttar, you maybe get 10 candy (or 20 if you want to pinap berry it which is a little risky, but maybe worth it if you are really good at capturing raid bosses).

Evolve the newly hatched Larvitar as it only costs 25 extra candy. Its near perfect! I would take that as a lesson not to evolve unless you can take your mon' to its final evolution stage as you may get better IVs by the time you accumulate enough candies..

The Attk 15 is a better one to evolve. Maybe you'll hatch a bleh Larvitar while you're walking this one to get 25 candies.