I faced the same choice in 2007 (same flying school I guess).
I chose the Grob.
Reason- I was told that it was a more challenging aircraft and that learning to fly in it would improve my skills. Also it was argued that I would find converting to other types easier than if I trained in the 150.
Since then I have been checked out on the 150 and PA28.
For handling qualities I would choose the Grob every time.