Please research first each macro's purpose. I believe that the \dotsX macros are for math mode, whereas \ldots works in text mode. The horizontal spacing is different in the different modes, so both macros may be appropriate in their respective contexts.

From https://tex.stackexchange.com/questions/77737/dots-versus-ldots-is-there-a-difference :

"in latex.ltx, \ldots is equated (\let) to \dots. so in text, it's the same, and you can use either.
with amsmath, the situation is more complicated; \dots tries to determine by context (only in math mode) whether to use \ldots or \cdots"

... and \dotsc just means \ldots (the kind of dots you use for comma-separated lists; in math mode only).

OK - looks like we can use either, then. That said, I like keeping \dotsc in math mode because it's nice and self-documenting (but maybe that's just because I used to typeset a lot of maths). I'd be happy to use Ams-dots in math mode and "raw" dots in text mode.