H-110 was my "do-all" for pretty much every magnum I load. In one of the last powder shortages I couldn't find any and gave Ramshot Enforcer a try.
This from what I understand is the same stuff as Accurate 4100, just like H-110 is W296 and HP-38 is W231. The Enforcer burns a bit cleaner for me vs. H-110, although the 110 wasn't bad if you keep one thing in mind... it isn't made to be loaded light, it's a typical magnum powder that likes mid-range published data and up with a decent crimp. Since you were using 2400 and mention the hotter loads part, you are likely already aware. I don't see mention of what type of projectiles you're using, but this or the Accurate 4100 variety should give you similar results to 2400 and will likely be cleaner.
As for the 38 special, HP-38 is always my go to on that one. I like Unique too but can't say its the cleanest.
I think it's worthwhile mentioning other brands besides the "old faithfuls" since selection may not be ideal where you are. Ramshot Zip works well for velocities similar to HP-38 and from memory burns clean. True Blue and AA#5 (my HS-6 replacements in some calibers during same said shortage) will work good in the 357 and will be fine in the special as well for upper end loads, AA#5 stands out for me on 38 +P.
There are quite a few good powders in this range that would likely suit your needs for both, Blue Dot and CFE Pistol are worth a look. If it works really well in the 38 special however, it may not be great at producing those upper end velocities in the 357. As already mentioned, the slower powders in the 38 are more prone to leaving unburned powder, will be trial and error for just about anything to see what's actually the cleanest. Part of the fun.