I also have a 38 inch waste and am in between sizes. The medium AbenaM4, Dry 24/7 and Tena Slip Maxi all fit perfectly for me. I'm yet to try North Shore, but that's coming at some point in the future.
For Tykables, ABU, Diaper Conn and Bambino... I am in between sizes. Which sucks for me, since my girlfriend (who refuses to admit she is ABDL even though she wears diapers more than I do now, and wears onesies and uses pacifiers routinely) only wears ABDL diapers, so I have to stock the house with both! $$$$
I think the ABDL diaper companies are a little skimpy on their dimensions as all of them seem to only work if you're on the smaller side of the fit scale. I'm hoping at some point, they make the wings of their diapers a little bit longer. Would solve all the problems without compromising anything.