IMO it all depends on what you are intending to do with your fuge. How much L.R. do you want to have in your main display verses how much to keep in your sump/fuge? How much cheato or what kind of critters you wanna keep in there as well (fish etc) questions of that nature can be a help in deciding whether to have a larger fuge or larger return section.
I hope i did not just answer your question with a question
but just some points i considered when I designed my sump.