Wow I feel like I'm gonna give an unpopular opinion here. But I want to go with Pikachu. I mean, have you seen a baby Pikachu before Pichu was a thing?
I would have to say Togepi, if only because Pikachu is shoved into your face so much that if I ever found it to be cute, which I don't think I ever did, I do not find it to be so now.
Oooooo this question hurts lol. I think they're both pretty cute, but I'm ultimately going to go with Pikachu because I think it has the potential to do more cute things, if that makes sense? Like, Togepi, it's a little egg with teeny tiny, barely functional limbs, while Pikachu's design allows it much more movement. For example, a Pikachu can hop off a table and onto my shoulder. That's cute. But if a Togepi hopped off a table, it would not land on my shoulder. It'd land on the floor. And it'd probably cry. That's not cute. That's just sad. I would feel bad.