I am currently studying a masters in scottish history, but would like to do another masters in a field I am interested in. I have narrowed it down to a MA in either intellectual history or in the classics. I would like advice on which one to choose for a future career as a historian. I think the intellectual history is more appropriate but that the classics would look very good on a cv. I do not know what I plan to do my PHD on. Is it advisable to do both, or can a person have 'too many masters'?

I wouldn't bother. If you're going to do a PhD, then save your interests for that. Another MA is just going to cost you money and in all likelihood won't particularly helpful towards PhD applications.

Unless you have unlimited cash and can afford to pursue it for intellectual stimulation alone, in which case, go nuts.