Always try to take off with a head wind. It reduces the takeoff distance required. Aircraft can take off with tailwinds. As a rule of thumb, the faster the unstick (liftoff) speed, the greater the acceptable tailwind component. Up to about 10kts.
Before I go into slope limitations I need to define a couple of things:
TODR: TakeOff Distance Required. Distance from stationary to flying 50 feet above ground.
ASDR: Accelerate Stop Distance Required. Distance from stationary to just below V1 (maximum speed to abort takeoff e.g. if an engine fails). Then abort takeoff. Then stop the aircraft on the ground.
Slope limitations are +-2% (I think this is a certification thing. It's certainly not a physically limiting factor)
Up slope:
-TODR increases (harder to accelerate up hill)
-ASDR increases (harder to accelerate up hill, but easier to stop)
Down slope:
-TODR decreases (can accelerate faster down hill)
-ASDR increases (can accelerate to V1 faster, but deceleration is slower)
I've not done the calculations, but I'm pretty confident that the down slope option is preferrable.
Practically, it's not up to the pilots. ATC tell you which runway is in use, usually dependant upon the wind. Then you decide if you can go or not. If it's a no go, you do the calculations there and then since the results will vary depending upon how much head / tail wind and up / down slope there is.