I'm probably being unfashionable here, but I like the PA38 as a training aeroplane. For the following reasons;
- Good visibility
- Good ergonomics
- Mildly unforgiving handling, which breeds good flying skills
- Low wing loading, which bounces around a bit in turbulence, and again breeds good flying skills.
- Cheap to run
- Hard to break.
For my money, the C172 in its many flavours only really has the last of these advantages. It is a very safe aeroplane, but it's big, heavy, over-complex for a basic trainer, and the main handling deficiency is that the control forces are fairly high - but that doesn't necessarily make for a safe pilot when transferring to something else.
So, I'd personally stick to the Tomahawk.
G