I have Tangent & ZCOs, had Kahles, have/had ATACRs and others.
Tangent has slightly better resolution, depth of field & field of view, and their turrets are the best out there. In my experiences, the optical IQ advantages of the Tangent are very slight compared to ZCO. Very slight. The "wide view" of the ZCO is noticeably better than Tangent - hard to explain as ZCO does not have better FoV. I prefer the ZCO reticles, and they have more turret options (15 mil/rev locking, 15 mil/rev NLE, 10 mil/rev NLE). Personally, I prefer the overall package of ZCO compared to Tangent, but I do and will continue to use Tangent for certain set-ups. And price has no bearing on that preference (scopes are very cheap compared to barrels, ammo, gas, time, etc). I don't know what the OP's hold-up is with a 36mm main tube, but rings/mounts are cheap.
Kahles is not in the same tier as Tangent/ZCO. New prices of Kahles are a rip off IMO, but you can save quite a bit compared to Tangent/ZCO if you shop for a used Kahles. The new K328i may change that, but only time will tell (also 36mm main tube).
My ATACRs have been a down from Kahles optically as well as in terms of controls & precision of mechanics. BUT, I haven't owned the 7-35, which by all reports is the gem of the ATACR line in terms of optical IQ. I've seen several used 7-35's go for ~$2,500 on a different forum. I wish the 4-20 ATACR didn't tunnel so bad, as that would've been a great crossover candidate, but a 5.5-20 isn't appealing to me.
The 6-36 S&B PMII is interesting, but their reticles are the hold up for me. Sounds like the 6-36 can hang with TT/ZCO, but I can't say from first hand experience.
If you are really unsure, go buy used and try it out. Get experience with it to develop your own opinion, and worse case is you sell used & loose little-to-no money when you move on.