There is no one answer. It depends completely on the name. Check both in Google to see which has the higher number of listings, and by how much. Overture is no help, they combine S & PL in their results, but there is another paid service that would tell you which gets the most searches.
In the end do the sound test - say the names aloud and see which (or both) sound good - or buy them both, especially if you are developing.