which do you think will make the most impact?
I think it depends on the person and their level of skill. I had an EXCELLENT pilates instructor and I had great results. I went through three personal trainers and the one I was with longest I gained weight with. The other two I wasn't with long enough to tell but one of them seemed to try to have us do exercises too fast and I didn't feel that was good. I tried another pilates studio after my great instructor moved away and it wasn't nearly as good. In fact, the way they were having me do certain things was hurting me.
So just in my personal opinion I would say just try both and see what works best for you.