I think Pikachu is absolutely adorable! I love Pikachu's contribution specifically in the anime, its bond with Ash is heartwarming to see! Also, I don't think there could be a better mascot for the brand. However, I do feel that Pichu and Raichu are somewhat underrepresented in comparison to Pikachu.
Unlike some, I actually am fond of the Pikachu "copies" that are introduced in each region. This is because I don't really see them as rip-offs of Pikachu and I think that the majority of them have interesting design concepts. Pachirisu is my favourite by far, it's just a bundle of cuteness.