I believe Geisinger's program interviews the top 15-20% of their MBS class (with decent MCAT score), but I don't know if that's a guarantee or not. There is some crossover between the medical school teachers and the MBS so you might be able to snag a nice LOR if you apply to geisinger later.
Upenn states they have linkages with other schools, but I am not sure how true that is or at least how those schools truly look at the program. They seem to have a lot of resources for other parts of the application like ECs, essays, resume etc. but since you are looking to prove you can withstand the rigor of medical school not sure about this one.
Georgetown's SMP is one of the oldest and rigorous of the bunch, and they have the added benefit of being able to take actual MS1 classes and being graded on that curve.
Of the three I'd imagine most people will tell you to do Georgetown's SMP, but to be prepared to kill it because not doing well in that program can be detrimental. Big risk big reward kind of thing. My ranking would be Georgetown, Geisinger, than Upenn. Best of luck.