UMASS!!!
Lets start with rankings (if they really matter to you): Umass is #3 primary care and #46 Research. Georgetown is unranked primary care and tied with Umass in research.
Price: Umass cheap as sin (avg debt ~$80,000). Georgetown: sinfully expensive (avg debt ~$128,000).
Personal Experience: Worked with a post-doc who came from Georgetown who said the place was falling apart due to lack of funding. She told me that they were getting rid on a large amouint of the non-tenured positions, and that in general it was not a pleasant place to work. Furthermore, it appears that UMass is a school that is on the rise, with improvements being made in the facilities and curriculum year after year, and its research ranking improving continually as well. Geargetown appears to be on a different trajectory however...
Even if the schools were the same price I would still choose Umass over Georgetown....and since they are decidedly different in price, Umass is the easy answer. Maybe Grandma is going to recognize the snazzy sounding name of Georgetown and feel slightly prouder of you, but hopefully that doesn't matter to you too much and you choose the better and cheaper school...UMASS