Seth and Alexa's place was fantastic. Spacious, modern, super clean, and nicely decorated. The shower was fantastic and the memory foam bed was super comfortable. Lots of nice little touches too -- Keurig machine with some K-Cups, plenty of towels, extra blankets if you need them. There's a nice coffee shop right next door, and it's literally a block from the BART, so super convenient to get downtown.
As a few others have mentioned, the sound isolation between this unit and the upstairs is not perfect. You can hear some footsteps and voices from upstairs, but everything was always very quiet by bedtime so no problems getting a great night's sleep.
Other than that, I can't recommend this place enough -- it's one of the nicest AirBnbs I've stayed at in SF.