They seem close to evenly matched. Interestingly, both seem to have some brighter spots that could potentially be considered a place where most of the mass is, but I am unable to discern a nucleus for either one.
Data from the following proposal is used to create this image:
Establishing HST's Low Redshift Archive of Interacting Systems
All channels: ACS/WFC F606W
North is 26.1° counter-clockwise from up.
