I have had seats all over Massey Hall since 1973 and I would take the J15 seat.
The interactive function shows the sight lines from all over Massey..
http://www.roythomson.com/mh_seatingplans_popup - just click on the area and you can see the view you will have. 10 rows back in row J and in seat 15 which is an aisle seat would be my choice..
even seats in the first balcony - two centre sections and the sections adjacent and as far back as row 8 or 9 are great seats. terrific sightlines and the sound is the best up there..especially near centre..
even going one more section over in the balcony are good..