I picked abortion because it is an intrinsic evil: it is wrong always and everywhere, unlike either war or poverty.
I would dispute that many wars are fought over resources and land, but those that do do not necessarily stem from poverty but greed for more land, resources, power, or riches. Mostly poor people don’t have the resources to fight a war.
Another thing to consider is that there are at least two parties to a war, and mostly one has been attacked unjustly, which means that one party is fighting over whatever their greed is impelling them to fight for, and the other party is defending itself. We will have war as long as we have bullies in the world.
WRT poverty, I think that altho a higher number of women obtaining abortions are poor, a higher number of women who have their babies out of wedlock are also poor. So, being poor is not a determinant of having an abortion but of getting pregnant.
So, if I could, I would first choose abortion, and then artificial birth control, which is, as the Pope said, the source of abortion, as well as a lot of other evils.