Most important domestique of the ones mentioned is surely Kreuziger. I can't imagine how much time Contador might have lost, had he not had Kreuziger in the mountains in TDF.
Porte was totally unnecessary for SKY all year around as a domestique. In his case, it seems like it would've been a better idea to just focus on a GT instead of helping a teammate (Froome), who doesnt need help...
Kangert did an okay job in the giro, but only showed in flashes what he was able to do as a super domestique.
Kiriyenka was oddly invisible this year, and I actually only recall pictures of him leading the peleton up a smaller climb on the first stage of Vuelta a Pays Basque. IMO he doesnt deserve a spot here, compared to others.
Other mentions: Devolder (did a fine job, even if he wasnt there for the final in RVV and PR), Kiserlovski (some1 else mentioned, was very valuable for Horner in La Vuelta), Bennati (a bit overlooked, has done a good job all year as road cpt and produced some small results himself), Stannard (Not as visible as last year but did alright again this year, great MSR by him)