oook i'll try since no one else has responded much
First off, both UVA and WashU are great schools. So you aren't going to make a "bad" choice. Secondly, I'm going to UCLA, so I'm not a biased WashU/UVA student.
If it were me, I'd go to UVA. The history behind the architectural program there is SO rich in tradition; Jefferson remains to this day one of the most revered figures in American history, and the fact that he drew the original plans would be an inspiration to any architect lucky enough to attend. The campus is beautiful, and VA as a state is just typically nicer than Missouri. UVA also has a more renowned reputation nationally and internationally; WU is fairly new to the "big stage" of prestigious universities. Some professionals say that WU is overrated, as in that it shouldn't be ranked that highly...while I'm not a fan of calling universities "overrated," the stereotype does exist, rightfully or wrongfully so. WashU has a more regional reputation, whereas in my opinion, UVA has a more national one.
Also, UVA is a close-knit community, due to the rich history and athletic success the school enjoys. There's just a certain feeling one gets at UVA that I think is very unparalleled. It's so
unique. As an international student, no university could represent the American dream, ideals, and work ethic better than UVa. It's simply America's university.
But again, both schools are very, very good. I'm sure if you went to WashU, you'd get a great education there. But at UVA, you'll be part of a special environment. And, you can take liberal arts courses as well, to supplement your major.
Good luck!