it depends ON

I'm guessing this was intended as a reply to my comment on the weather being sunny in Spain! 'Depend' is followed by the preposition 'on'. So you'd say, for example. 'Is is always sunny in Spain?' 'Well, it depends on which part of Spain you visit'. In fact, it's possible to miss out the preposition entirely in a sentence like this, e.g. 'It depends which part of Spain.' is also correct. But if you do use a preposition, it has to be 'on'.

It depends on is the correct choice.

It depends on the rest of the sentence and what you are trying to say.