I absolutely adore Pikachu and Raichu. Pikachu is cute, smart, and cheerful, and I've got a giant Pikachu plush. On the other hand, Raichu is more reliable in battle, as it's stronger (unless you count the Light Ball), bulkier, and faster. Alolan Raichu is very cute, and it has a neat typing.
Pichu, on the other hand, is the weak link of the line. It may be cute, but it's less reliable or iconic than Pikachu and Raichu.