Hi likair,
It would all depend on what gives you the best overall combination. Ultimately you would be able to get that answer from the applicable aircraft's take-off graphs.
The following figures are from a C172 (sorry, it's the only figures I could get my hands on this morning), but the same principle would apply to other aircraft.
TAKE-OFF DISTANCE FACTORS
2% uphill slope - 10%
Tailwind component of 10% of lift-off speed - 20%
Unfortunately the C172 manual does not specify what advantages a headwind or downslope would give you.
If, for example, you want to take-off with a 2% uphill slope - a 10% increase in take-off distance - but you have a headwind that will give you a 15% decrease in take-off distance, it will obviously be more advantageous to take-off in that direction.
The same principle applies to downwind take-offs. If the decrease in take-off distance due to the downslope of the runway outweighs the increase due to the downwind take-off, it will give you an shorter take-off distance overall.
NB: It is important to remember if you choose to take-off downhill with a tailwind that your stopping distance will be greatly increased should you decide to abort the take-off!
All-in-all you will have to spend some time with the graphs to get the best option for the day.
Hope it helps,
Prop Job