I posted a topic like this a few months ago. And though nobody responded, I realize now that the list in that topic is more of a postgame list than an efficiency list. So I figure that to try to help whoever might be trying to go through this game by at last laying the groundwork for such a list. And in regards to some tier spots, I have an idea for three or four tiers that, while consisting of Digimon that you'll definitely see lategame, I don't know if they should be placed between someplace like mid and low, or in an "ungrouped" zone. Even even considering that they'll likely look like this.
GBA FE Lord promotion tier
Mastemon
Creepymon
Barbamon
Beelzemon
Belphemon Sleep Mode
Belphemon Rage Mode
Leviamon
Lillithmon
Dratini tier
Lucemon (all forms)
FE13 Spotpass tier
UlforceVeedramon
Magnamon
Armor!Rapidmon
Examon
Dynasmon
Crusadermon
Leopardmon
Craniamon
Kentaurosmon
Gankoomon
Jesmon
Gallantmon
ChaosGallantmon
Alphamon
Omnimon
Imperialdramon Paladin Mode
DLC tier
Dianamon
BlackWarGreymon
MetalGarurumon (Black)
Omnimon Zwart
Beelzemon Blast Mode
Kerpymon (Black)
I'm also wondering which Digimon should be listed on most of the list. Should I have all Mega/Ultra level Digimon like with the other list,vwith consideration given to the fact that every Digimon in the game can eventually become any Digimon? Or should I give a focus similar to what Smogon does with their Pokémon tier lists and list earlier stages and tier them by stats, availability, and evolution? Any thoughts?