Canadian medical schools will be most highly regarded because of competitiveness of entry and similarity to the US curriculum. Following that would be British medical schools with the big names leading and then followed by schools in Ireland, Australia, New Zealand and Israel.
All options are very expensive and hurt you in terms of getting back to the states. If you are a very competitive applicant (GPA 3.8+, MCAT 34+) you can consider UofT, McGill, McMaster and Dalhousie in Canada as these schools take international students. Otherwise consider the UK, schools like Cambridge and Oxford will turn heads, Imperial, UCL and Edinburgh are also well regarded. Otherwise, most other medical schools in the UK will probably get a similar reaction.
Ireland and Australia have some very good schools but tend to be lower on the competitiveness scale for American students as they tend to take a lot of international students, often for financial reasons.
You will however find that reputation is not very important even to American PDs. Sure an applicant from a prestigious school may turn heads but it would come down to your tangible stats, like your Step 1 score, LORs and CV that really determine your chances. No one will pay much heed to a school's reputation since it has very little role in who you are as a person.