The DFA 100 works very well but might be a tad long for some shots. The DFA 50 is another excellent choice as is the DA 35 Macro. All of these are going to render colors well and also give you a good flat field with no added distortion from the lens. I love the FA 77 and FA 31 but I would probably lean towards the DFA 100/50 and DA 35 giving you a range of options. If you can only get one - which fits into your current lenses best?
DFA 100:
(I don't own the DFA 50 or DA 35 macro)
F 100 (similar to the DFA 100, same optical formula. My copy had element separation which made it more like an f4 lens or an f2.8 with a touch of softness):
And a few more with the DFA 100:
https://flic.kr/s/aHskuEBrPk