I have lived in a Fairlington townhouse for 6 years and love it! We are a family of 2 adults, 1 tween and 3 pets. It does feel small at times, but it's livable and cozy. People are very friendly and there are always people out walking dogs. Our location is very quiet, though we passed on a handful of places that were too close to the highway for our liking. We can hear our neighbors through the shared wall, but it's not loud. The multi-unit buildings may have more neighbor noise.
Depending on which condo association you are looking at (there are 7) there may be some drama on the Board. You can get involved or completely avoid. Parking is not a problem where we are. There are lots of community events, great swimming pools, Farmer's Market in the summer, close to Shirlington, beautiful garden like setting. It's really a great spot! I highly recommend it! And if you don't totally love the location by the highway, there are always new units being listed. We probably looked at 5-6 units from March to May and made an offer in May.
I might also recommend working with one of the local realtors familiar with Fairlington. Maybe start here
https://www.facebook.com/groups/fairlingtonrealestate