Guava is the quiet one in the fruit bowl, and I think that's why it took me so long to actually juice one. Cut it open and the kitchen smells like the inside of a tropical greenhouse, and the flesh is thick enough that the juicer fights you for it. Pineapple sorts that out. It brings enough water to loosen the guava and just enough sharpness to stop the glass tasting flat. Two guavas and a quarter of a pineapple is all it takes, and you end up with around 250mg of vitamin C a glass, which is well past what you need in a day.
Pink guavas give you the prettiest glass, but white-fleshed ones taste just as good. If your guavas are still firm, leave them on the counter for a day or two until they give slightly when pressed. Ripe guava smells sweet and floral before you cut into it.