Help me: what last perk should I use?

Depends on how good you are with chases, if you're struggling in chases nobody would hold it against you if you ran Windows of Opportunity- hell, even if you are good with chases- WoO will still have a positive impact in that your chases far more efficient, simply because you know exactly where to run, which tiles have spawned with pallets or windows and which haven't, which windows are blocked off and which are open, etc.

If you feel you're getting tunneled too frequently however, you'd obviously probably consider DS instead.

The end all comparison is this:

WoO will consistently improve your chases, (and thus perhaps your games as a whole) since it is active in every match at all times. Whereas Decisive Strike has the potential to have a greater impact on a specific match- but you may not get the opportunity to use it most matches.

So at this point it's really a question of value- which do you value more, consistency, or impact?

Also, somebody tell me what the hell CoH stands for, because I don't think I've ever seen anyone use that acronym. I even looked into the wiki and the only perks in existence that start with the letter C for survivor are Calm Spirit, Clairvoyance, Corrective Action, and Counterforce. Now I'm left wondering if I've missed something for the past five years.

WoO will save your ass more often and will buy your team more time in general (all the time you would spend running to already broken or not even spawned pallet or window that spawned blocked - basically a hit or down for a killer which this perk will prevent multiple times per trial). Information perks are ridiculously strong.

DS does not help in most of the cases anyway and is pretty much useless when people play smart - simply not unhooking in the killer's face.

Lol I'm just dumb

(but that explains why it wouldn't have shown up in the wiki, because it'd be under B not C...)

Run Small Game if you're struggling with finding totems. Although it might seem like a waste of a perk slot, the increased value you'll now get out of Circle of Healing makes it worth it, since you'll be wasting less time running around looking for totems in the first place and you'll be much quicker to react to the sudden disappearance of your first blessed totem and will be able to quickly place it in a different location.

Although small game can sometimes be disorienting, especially on maps with multiple layers / levels, so you may consider an alternative like Detective's hunch instead.

As for resilience, it boosts your action speeds by 9% at T3 which is something like 7 or 8 seconds off a generator if I remember correctly, so down from 80 to 73-72 ish. X 5 is a 35 or 40 second total difference across 5 generators if you were to be the gen jockey working on generators all the time.

Not to mention boosting the action speeds of vaulting, healing, unhooking, cleansing, unlocking, etc. on top of generator repair speed.

It's not a bad perk by any means it's actually pretty good, the only problem is the condition on which it activates- you must be injured at all times in order to get the maximum benefit and this can be a detriment if you're not good at handling chases and you go down quickly. It also becomes less useful when you're up against Killers with One Hit Downs built into their kits like Leatherface, Hillbilly, Ghostface, Myers, Oni, etc. because you're not getting injured you're going down right away.

Equipping Resilience usually means you've got something to compensate for that weakness of being injured all the time, so you've got Self-Care, or a Medkit, or even what you're running right now Circle of Healing. These perks will allow you to stay injured during the match without the fear of actually being totally injured- because you can keep yourself at 99% and then heal the last charge just before you engage in a chase with a killer. So keeping Circle of Healing and Resilience is a smart choice along with any of the other synergies I mentioned, and running resilience without them can still be okay you'll just have to be much more wary and conscious of how you play during the match in order to get maximum value out of it.

EDIT: The reason many people aren't running Resilience is because while it is a good perk, it's not the best perk in the world- there are plenty of perks out there that are flat out just better options in general, and the shortcomings of Resilience probably ward some people off as well. Not everybody wants to take the risk of being injured most of the match to take full advantage of a perk, and not everybody wants to tailor multiple perk slots for the purpose of maximizing the efficacy of resilience either. So I wouldn't say this is an entirely accurate indicator of whether it is good or not.

Funnily enough, Otz posted a tier list a couple days ago of ALL perks in DBD as of the current patch 5.4.0. and he talks about all perks in-depth for killer and survivor in this video. The timestamps for each perk are in the description below his video, but I'll let you know ahead of time the Resilience timestamp is 13:33:52. I haven't watched this entire video myself (for obvious reasons) but I did watch the Resilience segment and Otz has good things to say about the perk. He's always been a really solid source for information anyway.