Actually, one of the great aspects of italki is that I can have instructors with different dialects and accents so I can get exposure to a wide variety of Spanish, by having sessions with instructors from Spain, Mexico, the Caribbean, Central America, or South America. 

I don't think one is right and another is wrong. I think it depends on your situation. For instance, as someone living in the United States, I think it makes more sense for me to learn a Latin American style of Spanish rather than the European style. Also, just numerically, Spanish speakers from Spain really only make up a small percentage of the world's total Spanish-speaking population. At the same time, I'd like to be able to communicate comfortably with Spanish speakers regardless of where they are from.

Likewise, for a lot of people, it makes more sense to learn American English rather than British English. But again, it depends on your circumstance. 

I have never studied French, but for some reason, French seems like a different story. It seems like people tend to favor learning European French over, say, Canadian or other varieties.