Personally I hate Tomahawks with a vengeance.
I think they're nasty, tinny little machines and I would therefore say go with the nicely-equipped Skyhawks, HOWEVER....
a) You can bet your bottom dollar (and a few more as well) that the 172 will be significantly more expensive over the amount of time you will need to complete the course and
b) There aren't many aircraft you can hire relatively cheaply that have that sort of equipment so you'll find yourself hiring stuff with clockwork steam-driven kit (and you'll need to know how to use it) unless you are prepared to fork out megabucks.
So my answer to you would be to stick with the PA38 for the majority of your training for the cost and the knowledhe but give yourself a few hours for the fun and the experience of all-glass, which IS fun
