what do you think is the most babyish adult diaper you have tried?

In Europe Molicare Premium elastic or Tena flex. These are most similar to modern baby diapers with elastic wings. And of course, they are more comfortable.

My most babyish diaper I have tried would be ABU Littlepawz. They make me feel like a big baby when I wear them. The capacity is very good. I have woken up with a very swelled up Littlepawz, and still had a dry bed.

I believe the original SDK's were probably the closest to an actual baby diaper in its design. I prefer a diaper that has a higher rear and one where the padding is squared instead of rounded. It seems to be common now where the rear padding is more rounded. The squared look reminds me of the 90's Pampers design.

I work in China and have visited a few personal hygiene factories that make diapers and to my surprise, some of the more popular AB diapers being sold today online are being made by the same companies. If you have an opportunity to visit the fall Canton fair in Guangzhou, you will see many diaper producing companies advertising products they make for companies all over the world. In all cases, these factories make a generic version of the same diaper they will sell locally or to other interested parties. The only difference is that there are no prints on them.

Probably ABU Kiddo, I think that they remind me of the current Pampers Baby Dry diapers as far as the print goes, and then the single tapes.
I was also a big fan of the original Snuggies Waddler, the pastel print was subtle and that felt very juvenile to me. The new tykables are so much brighter, and those are less babyish to me.