I agree with Teddy B.
All players are going to go through streaks. If you can figure out when that's going to be, great, but it should all even out over the year and even each week.
What I mean is, some of your players will be hot, while some will be cold. Sure, it would be AWESOME if all your players were hot at the same time, but that's not likely. Just like it would be horrible if all your guys were slumping at the same time, but fortunately, that's just not likely.. unless you drafted a really brutal team.
In short, I would just go with the better player, although picking up a guy while he's real hot can be a great boost.