Ross (or Big 3/4/5 Carib) trumps MU-Sofia by a lot. At Ross you've got 50 state approval, a program that is two years shorter, USMLE preparation, federal student loans, US clinical experience throughout years 3 and 4, and (as much as Carib students will complain) at least some semblance of organization.
You are in a much better situation at Ross than at MU-Sofia. Especially with the bomb about to drop in 2015/16 with the equalizing number of US grads and PGY1 positions? Heck, depending on when you started, you might actually end up with a US residency for your trouble. I don't think that will be the case for most North Americans opting for MU-Sofia from here on out, no matter whether they study in English or Bulgarian.
Good luck at Ross!
"To array a man's will against his sickness is the supreme art of medicine."
- Henry Ward Beecher