That will vary from update to update.
There is no way to tell if there will be more potential bugs/balancing/tweaking to iron out in the Mountain caves update, or the new Mistlands biome than in the Hearth & Home. You'll have to treat each update independently. That said, I would expect Mistlands will require a lot more testing than anything yet released, given the scope of a whole new biome and all that it entails.