I think for me its a question over which is the best training aircraft - I personally like the Tomahawk for training as I think it also comes with some handling traits and vices (some I like, others I dont), and on balance I think it is more likely to make a student more 'pilot' aware than perhaps a forgiving Skyhawk.
It should also help for next steps whether it be tail wheel or onto (glass panel) spam cans - you might also need to know how to use those steam driven dials when the lights go out on your PC!
Probably the biggest difference will be in the overall cost of a licence which will should be cheaper if you do it on the PA38.