It depends what you mean by "prefer". If you're EXP and have lots of miles, then ticket all three seats (2x4th, 1x5th); if another on the 5th comes up, then ticket it and cancel the 2x4th; if not then cancel the single on 5th.

If "prefer" means you're really going to fly on the 5th, even if one is milesaaver and one is aanytime, then forget about the 4th.