Miki is about the closest to a mascot girl SM has gotten so far. And she doesn't get a lot of support, but probably more than any of the other SM figures to date. She's still the #1 seller on CP. 

 

Apollo is older than M4. 

I don't know how true it is, but I've heard that both DAZ and SM (e-frontier at the time) offered to buy Apollo from his creator, which shows how well liked his design was. Again, don't know if that's actually true. And then a few years later, there's genesis.