I am thinking of buying either a salamander or razordron in order to have a crowd control unit. Im not sure who?
One on it's own won't do much, I prefer Razordons as they don't really need handlers as much as Salamanders do.
Razordons are objectively better/more versatile, but Salamanders have big rend - something Seraphon are sorely lacking. Against fatter armies like certain Stormcast lists, Salamanders can be put to good work.
The good news and bad news is that you will most likely want both! Especially because they make great summons!!
Yeah I think both have their uses. Depending on how popular Nighthaunt are, you might find Razordons more efficient against all their 'no save modifier' saves. Sallies are really terrifying though, especially with the potential for extra Mortal Wounds if you cause some unsaved wounds on the target unit.