Reading the reviews for landmark (particularly for sonoma suites online), we didn't know what to expect when we arrived. However, we had a great experience with landmark at sonoma suites (their building at 16th & Van Ness). The apartment is charming, and the kitchen comes fully equipped with the pots, pans, etc. that a person might need. The location was fantastic for us, and offered easy access to the mission. We had no issues at all with landmark either -- Our bathroom light went out during our stay, and they had someone come in to fix it the same day.
A few notes if you're considering staying here. This area of the mission has a lot of homelessness/poverty, so if that makes you uncomfortable, then it might not be for you. (We had no issues, and everyone was generally nice and respectful). Also, it's in an old building in a city, which means there are bugs/small roaches sometimes -- it just comes with the territory. Keep your apartment clean, and your food sealed, get a bottle of spray for when you see them, and it's really not a big deal.
Anyway, we loved the place, it was everything we wanted, and a completely reasonable price given that its San Francisco. Would reccommend!