If you want to set a new PR or a course to help you qualify for Boston or New York marathon then you need to look at this list of fastest US marathon.
1. Chevron houston marathon in Texas
2. Austin Marathon
3. Lincoln National Gurad marathon
4. Rite Aid Cleveland marathon
5. Grandmas marathon
6. Chicago marathon
7. Steamtown marathon
8. Philadelphia marathon
9. California marathon marathon
10. Las Vegas marathon
Factors considered in compiling the list were : Flatness, weather, size of the field and number of turns.
Source running times