I think it depends. Say you get accepted to both. Thats when I'd start asking questions.
"Who will I be working with?"
"What level of individual attention am I given?"
"How many others will my advisor be advising?"
"Where does the funding come? (fellowship? teaching? etc?)"
"How much leeway am I given in designing a course?"
"What are my opportunities for summer?"
"Am I in class with PhD students?"
"Any cross-department courses?"
"Travel funding?"
"Research funding?"
"What resources have you got for me? (Library, artifacts, etc)"
If it all comes out even ask yourself, "who has the best pizza nearest to campus?"
ETA: Also - what Proflorax said.