Personal favorites:
To min-max the land area covered by radar:
North America: Detroit
S. America: Lima, Peru
Africa: Cairo
S. Asia and Australasia: Hengchung, Taiwan (Southernmost tip of the island)
I typically start with Cairo and Taiwan for the sake of covering as many lucrative funding areas as possible, followed --- if I get that far --- by Detroit, to cover the whole continent of North America. These four bases cover pretty much what needs to be covered. This assumes that places within regions matter no more than any other places.
Any better ideas?