The major deciding point between Colmar and Lansdale is schedule.
Like Toobusy already pointed out, there are a decent number of trains on the Lansdale/Doylestown Line (the R's got dropped three years ago) that either originate or terminate in Lansdale.
As an example, if I'm going to a concert at the Wells Fargo Center or to a Phillies game during the week the Colmar station is not realisitic because the last train that stops at Colmar departs Center City before 10pm. Why bother with a station that gets skipped by half the trains after 5pm when two miles away there is a station that every train on the schedule stops at? It makes no sense.
Edited: 4:12 pm, April 17, 2013