The examples in this answer are sorted from most common to least common. You can decide for yourself how far you want to go.
To convey the meaning of ever in affirmative sense1 (as in "the best ever"), you can use "de mi/tu/su vida", which means "in my/your/his/her life":
Han sido de lejos las mejores vacaciones de mi vida
or "de la historia", which means "in history":
Han sido de lejos las mejores vacaciones de la historia
This last version is of course stronger, though it sounds a bit strange when talking about holidays, as holidays are an individual thing. It makes more sense when talking about public events:
- Fue el partido de fútbol más aburrido de la historia
but it is not wrong to use it in the "holiday" sentence for especially strong emphasis.
These are the most common alternatives. It is also possible to use "nunca" or "jamás" with this meaning, though they need to be accompanied by a verb. The phrase "que he visto nunca" is relatively common:
- Es la mejor serie que he visto nunca
- Es la mejor serie que he visto jamás
An even more poetic way of saying it is
- Es la mejor serie jamás creada
As far as I know, you cannot say
because "nunca" with this meaning needs to be modifying a verb.
1I assume this question is only about affirmative sentences. To use "ever" in questions, as in "Have you ever...?", you usually say "alguna vez", as in "¿Has estado alguna vez en Japón?"