I'll not be as outspoken against the PA28 but I do think something like the Tomahawk or 152 is better at teaching FIs. For example, demonstrating adverse yaw or the effects of power is far more difficult in a PA28. Stalls are far more benign with less opportunity to demonstrate some of the symptoms. As for landings, they didn't call it the 'Piper auto land' for nothing.
In summary, not a bad aircraft, just one that I think dulls some of the bits which are important to being an FI. If I had an FI looking for a job having done his course on a PA28 I would spend a little time refining his skills on a 152 before letting him loose.
Recommendations - the flying bit is the easy bit. The trick is being able to teach.