I own a C2700 I got earlier this winter. I demoed at my local audio shop the other two as well.
I felt of course you get more with the C12000 but i think you have to ask are you going to use all those features specifically the SS and Tube sides? I feel your getting 90-95% of what the C12000 can do with the tube side compared to the C2700. I didn't listen to the c1100 very much or the C12000 in SS.
Both sound excellent IMO and really unless the price difference is insignificant to you then buy the c12000 if its not then buy the C2700.
I really like the C2700 its not your old mans Mac its lively, extended, quiet even the MM-MC stage is dead quiet. they are also quite neutral not rolled off or mushy sounding.