I'm currently in the Georgetown SMP. Actually, last year I applied to both (and was accepted to) the Tufts MBS and Georgetown SMP. Both programs are good and probably similar (I've never taken a Tufts class, so grain of salt).
Pros of Georgetown:
-Really challenging med classes (6 total). This year is the most difficult thing I've ever done in my life, and this is coming from someone who did molecular biology at a pretty damn rigorous undergrad. Two-fold benefit: 1) gives you a preview of just how challenging med courses really are, and 2) gives you a chance to decide whether or not you still want to go through med school. Nobody will blame you if this experience makes you decide not to continue with medicine - it's an extremely difficult process, one that most people would not choose to go through; it's smarter to know early on whether or not it's truly for you. (I'm not discouraging you from medicine, just making sure you're aware of the rigor.)
-Good teaching, for the most part. You'll find occasionally crappy lecturers at every major research university, and GU is no exception. But generally I've been pleased.
-Friendly classmates - I found a good support study group very early on. Everyone knows they're in the same boat - the vast majority of people in the SMP are med school re-applicants - so you won't find anybody super pompous.
-GUSOM traditionally interviews about the top HALF of the SMP class based on their GPA in the SMP. (Be aware that this changes from year to year - it's probably closer to the top 40-45% of the class.) C/C that with Tufts guaranteeing interviews to the top 25% of the class. After the interview process, GUSOM will take mid-20s to high-30s of them.
-Most profs are very responsive to questions - every module employs an online forum where students can post questions and other students respond, and the profs DO chime in and correct errors.
-Experience. The GU SMP has been around for a LONG time, and the folks up top know what they're doing. In addition, all the SMP team leaders are also professors. More importantly, there are some med schools that are "SMP-friendly" and are familiar with GU's SMP, meaning if you do well and send your grades to those SMP-friendly schools, you'll improve your chances at an interview. I don't doubt that the quality of education of Tufts is good, but the fact is, the Tufts MBS is a very NEW program, and med schools likely aren't as familiar with it. This means that the grades from Tufts may not have as much clout with med school adcomms.
-Hybrid of Discipline-based and Systems-based curriculum. 3 years ago, GUSOM completely revamped their curriculum, and most of the med courses are now systems-based. For example, in the Cardiopulmonary Biology Module, you will learn about the anatomy, physiology, embryology, and radiology of the thorax/heart/lungs ONLY. Tufts (and schools that employ a Discipline-based curriculum) will combine ALL of Physiology as one course, ALL of embryology as one separate course, ALL of anatomy as another separate course, etc. I personally find Systems to make much more sense.
Cons of Georgetown:
-Large class size - this year is 180; combine that with the 190 M1's and about 20 GEMS (like SMP for underprivileged/minority), and that's almost 400 students vying for the attention of one professor. Tufts MBS is about half that size (~100).
-Advising. I'm on the fence about this - I've had good experiences with my advising, but only because I take initiative. Some classmates have the opposite experience. The advisors are VERY nice and knowledgeable, but again, sometimes it feels like they don't care or don't really know you because there's simply so many students.
-Rec letters. You are randomly assigned to a letter writer, some of whom might not ever teach a class to you. The rec letters all have the same stock form - describes the program, the grading system, what it means in terms of comparison to the M1's. You get one tiny little personalized paragraph at the end of the letter. You can imagine the problem when each letter writer meets with 15 students, for like 10 minutes each. Most people only meet with their letter writers once (you're always welcome to take the initiative), and if you're assigned to Dr. Suarez, good luck getting him to send out your letter before December.
-The Georgetown neighborhood itself. DC is an amazing city, but good luck getting to it. Metro does not come to Georgetown - it's difficult to get in or out. GU runs shuttles to nearby Metro stations, except on weekends, and there are some good Metrobus lines, but generally it's a pain in the ass. Tufts SOM is smack-dab in the middle of Boston Chinatown, where The T is easily accessible. (You may think to yourself you're only there for a year, but trust me, location matters - you're going to work hard, but you should get out a little too.)
-Possibility of Dual Degrees. GU SMP doesn't have the option, whereas Tufts has the MBS/MPH option.
Either way, both programs are extremely difficult, but if you can succeed, your chances of getting into med school will be significantly improved. More importantly, you'll feel truly accomplished - like I said before, it's a really hard path, but if you really want it, you'll get it. Good luck!