If you’re going to be commuting to WTC then I’d avoid Tien Mu. Traffic too and from Tien Mu/Shihlin is as bad as it ever was, and you could expect quite a long journey. Although the MRT and bus lanes have improved Taipei’s traffic on the whole, Tien Mu itself isn’t very well served by the MRT.
Besides, unless you’ve got kids in either of the foreign schools in Tien Mu, as an expat the area now holds little of the advantages over downtown, as was the case previously.
And I won’t even start on rental prices in Tien Mu. Suffice to say it is way overpriced.
Close to the WTC is the Yu Tswei San Chuang area- on the hillside next to Elephant Mt. and overlooking the city. It’s 5 mins to WTC, rental is very reasonable, the air is fresh, it’s quiet and the views are great. I currently live there and rate it highly. Furthermore, at weekends it’s not full to bursting with adolescents wearing ridiculous baggy pants shopping for 2nd hand clothes and ice cream. Go to Tien Mu at the weekend and you’ll see what I mean.