My son is playing travel but when he was younger we did MSI because we live in Potomac and that’s where all the school based teams played. Same for our now college son who played rec and classic. I think you’ll find the biggest difference is geographic. Most people we knew in Rockville, Bethesda and Silver Spring played MSI. People we knew in Gaithersburg and Germantown chose SAM. However, MSI has the worst fields for rec and classic soccer. I think SAM uses the MD Soccerplex. That would be a huge plus for me.