I’ll go with Pros and Cons here, as I like to do
•Can trap and defeat it’s most common counter, Eternatus, easily
•It’s ability to trap with block is very helpful against slow, passive Pokémon, as it can recover from Toxic with Rest
•The bulk boost from Calm Mind is incredibly helpful, and the SpA boost is great too
•Struggles against Ferrothorn
•You can easily be set up on, as it doesn’t pose as much a threat to OHKO
ResTalk Sheer Cold
•The threat to OHKO with Sheer Cold is very helpful, and can surprise OHKO things that try to wall it or set up on it
•ResTalk is it’s best form of recovery and can let it attack, while the other set doesn’t have room for Sleep Talk, and therefore can’t move while asleep.
•Somewhat luck based. It’s luck to get something good from Sleep Talk and luck for Sheer Cold to hit.
Situations where Block is superior:
Eternatus: Sheer cold does fine, but Block Kyogre walls it pretty much completely
Ditto: Ditto can hardly touch Block Kyogre, while it can try it’s luck with Sheer Cold against Sheer Cold Kyogre.
Special Sweepers: Calm Mind and Rest can be a major annoyance for many special sweepers.
Situations where Sheer Cold is superior:
Ferrothorn: Can go for an OHKO with Sheer Cold against it.
Groudon: Sheer Cold can get it out of there.
Various stallers: Sheer Cold can OHKO unsuspecting stallers.
I’d go with Block+Calm Mind Kyogre. It’s less luck-based, and is better in more situations.
Hope this helps!