What is your favorite rtv/gasket maker"?

I will not use RTV on cooling system parts. In field service its too hard to keep everything dry. Only OE application I can think of are some Toyota water pumps, I generally seek out pumps for those that use gaskets in place of silicone
On late-model Toyota timing covers, there is a coolant passage (or two) on the cover. When resealing the entire cover, the coolant passages must be sealed using a RTV that can withstand coolant.

Toyota specs 1282b for the coolant passage areas and 1207b for the remainder of the cover.
Remember there's a "mid-grade" Right Stuff with 90 minute cure which is barely more expensive than Ultra. Some WalMarts sometimes carry it, but less so since the irrational global panic of '20.

I'm pretty much always too cheap to pay for the 15 minute cure Cheez Whiz Right Stuff, although I completely understand it for the professional tech who's fast and proficient (none of which describes me)
the Right Stuff 90 minute still has the silly instructions of snug bolts in, wait 1 hour and torque to spec. However, it doesn’t require 24 hour cure and it does kick much sooner than Ultra/Optimum.
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It can actually expire fairly quickly - 1217H for Nissan/Hyundai usually expires within a month or two of when we receive it from the dealer. MB stuff as well, sometimes.

Some of them will harden when expired. Others will appear fine, but won't cure.

Hoarders beware.
With me 90% of goes in the trash after opening the tube so I buy the smallest possible tube, use it and toss it. Hylomar is my go to but RTV is still required in some applications.