Q. Which is better(during these covid times): to daven in a street/ backyard minyan b’rov am (with social distance) or in a beis medrash (that was allowed to reopen) with a mere 10? 
A. Horav Shlomo Miller’s Shlit’a opinion is that if you are in a location where Rabbonim and authorities have permitted both scenarios you propose, and after complying with all recommended precautions, if you are part of the ten, preferably daven in a Beis Hamedresh.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a