Hmmm. I'm a part-time instructor at Tayside so unable to give an unbiased opinion, however I can tell you the following:
There are no landing fees for Tayside students, either at Dundee or Glenrothes.
Good, well equipped aircraft, based at a commercial airport so straight into the ATC/commercial environment.
Very good simulator on site, and an agreement with Loganair to supply candidates for assessment, that uses that simulator for those assessments.
That said Perth is a nice airfield, so you should visit both before making your decision.