Like everyone else, if I had to pick one day it would be Friday though I wouldn't count out Thursday or Saturday before the front either if I had the time. A few days of a stable weather pattern is a rule of thumb for good fishing and pre-frontal conditions should be optimum.
As Gundog mentioned, Saturday could be a good day, and possibly one of the best as well. If the front comes in later on Saturday all hours before that should be considered.