Though I live in SanLiTun, I often recommend DongZhiMen (Especially GuiJie) which is nearer to everything else...
58.com , if you don't find anything you want, my suggestion is Scott
Hahahahaha ... I cannot help but wonder, why Sanlitun, or Haidian?
Like the argument that every race/country has good and bad people ... every district also has good and bad apartments ...
Are you asking for which district? Or which apartment block?
How much do you want to pay? How new do you want the block? What facilities do you need? etc etc etc ..
my friend was just asking to for help last week,he got a three bedroom apartment at guangqumen ,very close to subways station,he lives alone and he is looking for roomates now,but ,i'm not gonna recommend him to you since u r a beautiful girl ,haaaaaa,u know what i mean