I would say:
¿Qué fue lo más gracioso o divertido de todo lo que alguna vez hicisteis en vacaciones?
That's a lot of rules for one sentence... ok, lets start :)
First, we don't know what was it, what we are talking about, if we do, and we were asking for something specific, like what was the funniest story, or the funniest anecdote, or the funniest party, then we would say 'Cual': ¿Cual fue la historia/fiesta/anecdota mas graciosa, etc.? But we don't know, so we use 'Que'.
After that, we use 'fue', but you could use 'ha sido' too. In the first case you would be making a temporal reference, and depending on the case, saying that it has no more relation with the present. In the second case, it something that happened already, but it still has some relevance with the present... it's still the funniest thing you've ever done on holidays :)
I think the rest is vocabulary, and 'hicistes' was right already. Also there's no correction about 'alguna vez' (this is to clarify that it could be in any holidays of our life). I hope I was clear without talking too much, lol.
REF.: I'm a Certified Spanish Teacher.