I'd personally go with the Boutique, just to get the name on the resume, and then move back to Mexico if thats what you really wanted. The exit ops for IB is why people do it for 3 years, but if you don't think you can handle it, just go with the options in Mexico, maybe you can hit it big!
Unless of course having a job at an American firm doesn't mean anything in Mexico, then it is really just up to you and what location you want to work in.
Unless of course having a job at an American firm doesn't mean anything in Mexico, then it is really just up to you and what location you want to work in.