Johto Sneasel is better in NU
The Post DLC 1 Viability Rankings came out yesterday, with Sneasel being at B+ Rank, while Hisuian Sneasel is B Rank. Johto Sneasel has a nice offensive typing being a Dark/Ice type, with only opposing Johto Sneasel and Tauros-Paldean-Blaze (and technically Thick Fat Hariyama) resisting the combination. It also has access to Knock Off, which is one of the best moves in the game, meaning it can make progress against Pokemon who rely on their item as well as its checks. Sneasel also has Ice Shard to pick off faster Pokemon such as Jolteon, which is nice.
With Hisuian Sneasel, there are more Pokemon in the tier who resist its STAB combination such as Salazzle, Palossand, Weezing, and Gligar, meaning most teams have a Fighting/Poison check on the team. Because of this, its Swords Dance/Close Combat/Gunk Shot/Trailblaze set isn't as scary as it was since Pokemon such as Gligar, Sandaconda, and Palossand are in NU. Like you mentioned, Hisuian Sneasel does face competition from other Fighting-types. Hisuian Sneasel also has competition from the other Poison/Fighting type, Toxicroak. Despite it being slower, Toxicroak has access to Dry Skin and Sucker Punch, allowing it to check Bruxish.
TL;DR Johto Sneasel is the better Sneasel since it has a great offensive typing as a Dark/Ice type as well as having useful moves such as Knock Off and Ice Shard. Hisuian Sneasel's STAB combination isn't as good, with quite a few Pokemon resisting it. It also has competition from the other Fighting-types in the tier. This doesn't mean Hisuian Sneasel is bad; it's still useable, but not as the scary threat it once was.
