Sean's comments on the Monarchy and MF amps seem quite adequate. My personal preference is for the warm smooth character of the Monarchy SE 100s.
I believe the ARC D115 is an older, somewhat dated, tube design, which sounds nice, but exhibits a relatively high amount of noise in the form of tube hiss (certainly when compared to either of the other amps you've mentioned). Using the D115 with high efficiency speakers may disqualify it because of this intrinsic high noise.
I believe the ARC D115 is an older, somewhat dated, tube design, which sounds nice, but exhibits a relatively high amount of noise in the form of tube hiss (certainly when compared to either of the other amps you've mentioned). Using the D115 with high efficiency speakers may disqualify it because of this intrinsic high noise.