While I do not know those three flying schools I do know Highland Flying School in Inverness is very good and the airfield like Aberdeen is full ATC. What I would suggest is visit all of the posibilities and try to get a feel of the place and talk to other students there. It may also be worth enquiring about the QXC landing fee costs since they will be on top of the rest of the training, the south cost schools students end up paying arround £20 at each of the two airfields they have to land at for the QXC. I got Wick and Kirkwall for my QXC with landing fees arround £4 a piece.