Actually, I have to agree with the apostrophe thing. Misusing them drives me absolutely bonkers for some reason. It's right up there with nails on a chalkboard or rubbing cotton balls.
I would use "an SUV" but "a sport utility vehicle". So, go with the sound of the acronym.
Since this a grammar thread I'm going to point out that "SUV" isn't an acronym; it's an initialism. Acronyms are spoken as words (e.g. SCUBA), initialisms are spoken as letters (e.g. FBI).
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