AG, I haven't flown with ATI but their fleet is rather small. Island Air has 6x C172 (3 new) and 6x 150/152 so availability of aircraft is rarely a problem. I'd suggest taking an intro flight & tour with each school before deciding. No real advantage going with Toronto Airways unless Buttonville is closer for you- they charge the same as the schools on the Island.
You should also look into the community college programmes if you haven't already- GBC and Seneca both operate them (GBC uses the island, Seneca uses Buttonville), I think Humber has one as well.