If it's only sticking to Digivices, then the D-Ark is the one I would go with. If we take into consideration the v-pets too, then it depends. In terms of customization and features, my favorite is the Accel. In terms of nostalgia and design; the D-Ark. In overall fun and engagement; It's a tie between the DM20th (because of it's roster and it also has Dracomon) and Vital Bracelet/Digivice V.

My favourite are the D-Scanner from Frontier and the Xros Loader from Digimon Xros Wars.

While I don't really collect them in real life because I consider them too much of a gimmick toy for my taste, recently I got the Xros Loader as a gift for a dear friend of mine and I gotta admit the thing is pretty cool. Has an MP3 player and works with CC and DM cards. Also the built-in game. Hope Bandai brings a re-release for how good this one is.

For me it's Digital Monsters, Digimon Pendulum, Digimon Pendulum Z, and Vital Bracelet. Digital Monsters: The most simplistic gameplay and feature, they doesn't need frequent care, the background is lovely, and the screen is always on (so i can always watch them without turning on the screen). Digimon Pendulum: Love the field based roster, the more complex sprite animation, and same as Digital Monsters, they doesn't need frequent care and the screen is always on. Digimon Pendulum Z: Love all the newcomer Digimon on it (especially Sangomon and Manticoremon), the close up feature, and the pause feature (useful in busy time). Vital Bracelet: The first wearable device and also the shape is not flashy, so it's very convenient to carry it everywhere. The DiM Card is very useful so i doesn't need to buy another version to try another roster.

Dアークが好きです✨

My favourite was pendulum 98, vpet 97, d2, d-3, accel, d-scanner, digivice ic, xros loader, also many more I can't say it here..