The factory-unlocked version will not be available for a while in the US, only through carriers. Verizon's phones usually ship unlocked, but still have carrier bloatware and you'd have to check if the frequencies from your carrier are compatible.
The only way to get a factory unlocked version right now is through Amazon... but they're not cheap. AT ALL.
Amazon taking pre-orders for some versions of the Samsung Galaxy S6 and S6 edge | Android Central
At the current dollar exchange rate VS Mexican Peso, you might want to watch out for sellers bringing their unlocked phones either from Brazil or Europe (usually through MercadoLibre, that's where I used to buy mine when I lived there).
If you're on Telcel, the most compatible ones are usually from AT&T and T-Mobile. Movistar is usually compatible with T-Mobile, and Iusacell is most compatible with Verizon's.