The only time I paid attention was when I was on inhaled Tobramycin; they recommended the Big Green Machine (Pari Vios) with a specific cup but I don't remember the one because it was 6 years ago. Now I use the Pari Sprint or the reusable generic with my PariVios, my daughter's PariTrek (when we travel together) or my DeVilbiss Traveler.
I use the Big Green Machine, even though it's big and loud, when I have an exacerbation (or feel one coming) - it puts the meds deeper into my lungs.