Which lavitar to go for?

Nice nickname GOT fan? If you plan to use it as an attacker exclusively I'd go w/ 2 too saves you a ton of candy and stardust.

What's the IV breakdown? If it has high attack then the 71 looks good.

A bit difficult because the moveset you eventually get may be a determining factor in how you use it perhaps? Accepting that you intend to use it as an attacker I'd still go for 1 (82%) because it gives more options, and it'll max out higher when you get to level 38. This is all IMO of course, and it's thinking a bit longer term, which will come around quickly enough. Anyone, good luck with it, hope it's super cool for you, whichever way you go :)

Back when Gyarados was never really something you put in gyms and only viable as an attacker, I spent 400 hard earned magikarp candies evolving a 67% lvl 29 Magikarp to save on stardust. It seemed the right thing to do at the time, but when Gyarados suddenly ended up with 6th highest cp potential in the game, he's now useful to put in gyms. However, with only 67% IVs, he's 100cp behind the alternative I ditched, which was a 93% IV lvl 20.

I would argue that none of those are worth spending 124 larvitar candies on, unless they are pretty common to you. If you end up with Iron Tail/Fireblast, it might not be your #1 alternative for attacking, and in that case it might still be useful to put in gyms due to its high CP. Shaving is a big issue in my area, so even Snorlaxes get shaved off due to too low cp.

take the 2. it will be about ~3000wp high enough to stand in gyms and to attack as well. then wait for another one with
90%+ 15 attack and evolve it. if it got a good moveset -> push

I would try and find another with higher IVs. Those candies are too precious to use on one with anything less than 86.7% imo. All of those will have high cp, though you want one for offense anyway, but to me it's worth waiting for