Thank god this isn't gamefaqs, otherwise it would be a show of personal offenses between sazukeEX and misha-heart haha. IMO Donnel!Kjelle > Vaike!Kjelle=Gaius!Kjelle because skills>mods. Vaike!Kjelle is still quite good, though and I'd use it if I were using the FEMU, in order to be able to do Gaius!Nah and Donnel!Noire.
I'd never do Gaius!Kjelle, since hes the best non-mu father to the other girls in the triangle, while he's not the better kjelle father.
IMO it goes: Noire: Gaius>Donnel>>>>>Vaike
Nah:Gaius>Vaike>>>>>Donnel
Kjelle:Donnel>Vaike=Gaius.
Kjelle is the only one that works really well with all the 3.