ashdamn I am a pro PA38 instructor but to be honest it really makes no difference which one of them you choose both fleets these days are all old and tired.
Its all in the person sitting next to you that makes the real difference.
If you have a talent limited gimp of an instructor in either type of plane your not going to have a good time of it.
Personally I would suggest if you have the same instructor for both you have an hour in each and see which you find best for you.
But if the instructor doesn't like PA38's its not worth it. There is nothing worse than an instructor that ****'s themselves at the thought of teaching in them. You will end up doing silly fast speeds down approach just to make the instructor feel safe and the benifits you do get from learning in a PA38 will be lost on you because the instructor won't let you see them.
persoanlly I love instructing in the PA38 and think it produces a better pilot at the end of training but there will be quite a few that will disagree with that.