Referring to this : Usage of a comma for emphasis
I don't really get the difference between "—", comma and ":" in the case of putting emphasis in some sentences like this:
1- Don't forget, they could be tricking us.
2- Don't forget: They could be tricking us.
3- Don't forget — they could be tricking us.
If there isn't any difference between those, which one is more proper for using?
And another puzzling thing for me is: in each case ( 1, 2, 3) which part of the sentence is emphasized and has more weight?
(I think that my question is not duplicate, since I am asking about comparing three signs: "—", comma and ":". Which is not really answered in the mentioned "possible duplicate".)