A gift is a kind of one-shoot resource. It gives a boost of 30 at best, and only once or twice. After that, you get 3 or 5 for your money. The other means mentioned have a much smaller effect but they give a steady positive bonus in your relations. Bear in mind two things, though: You have also negative "bonus" for not being of the same religion and/or culture (which is a big problem for egyptians), and your offering of alliance needs a relationship of at least +150 or so to be at least considered. One way of granting a big bonus is to receive or to pay tribute, but there has to be a war first. Problem: to obtain a tribute in a war with a medium power is almost impossible (with a major you can drop the "almost"), and paying tribute costs you, aside of the money, a lot of autonomy in your diplomacy.