inline math with \ldots

Question

what should be preferred: $x_1,\, x_2,\ldots,\, x_n$ or $x_1$, $x_2$, ..., $x_n$ I'm hesitating for the \ldots versus ...

Answer 1

$x_1$,~$x_2$, \dots,~$x_n$

is OK.

This is how Knuth use in TeXbook.

For me, I would replace the tildes with spaces.

I don't think one should use ... instead of \dots or \ldots.