As a native of the area, both schools have good reputations... But also are known to be expensive (which is also true). From my research, SU has the superior program in terms of faculty, quality of education, and facility (you have to go into DC for Marymount's cadaver lab, meh). Also, while cost of living is expensive in both areas, you would be extremely lucky to find affordable housing close to Marymount's campus in Arlington. Luckily there is a metro stop close by. For SU, you can find affordable housing within 15 miles of campus, especially if you find roommates for an apartment before starting.
At the end of the day, I found SU to be a wiser choice financially and academically. I hope this helps!!
Also, if you choose SU Leesburg let me know!! It is likely where I'll be attending.
