Focal length is going to be a big part of this. Look at this image, and remember that we are comparing 85 and 115mm effective focal lengths (for portraits)
Typically, I would suggest that the DA* 55 is going to be better for looser portraits (upper-half) while the FA77 is going to be better for headshots and tight shots of one's face (as seen above). Different faces demand different lengths for optimal compression, however.
Now if this is to be a general-purpose lens, I would go with the DA 55 just because I find the mild telephoto more useful overall than something close to 80. However, for portraits, the FA 77 would likely pull ahead depending on your needs.
Last edited by paperbag846; 12-29-2010 at 12:38 PM.