Yea, I'm a fan but I can put my bias aside in any debate. I love Nintendo and have grown up with them for the last 15 years about, but I can still debate how much better the 360 is compared to the Wii. Even though I love SMRPG, I don't see Mallow having as much of a chance of becoming a playable character. Sure, he would go along with GEno, but Geno was much more developed and has an enormous fanbase, which Mallow did not. Geno just fits the bill.
I played 10 minutes of Metroid for GC and don't like the Metroid series, but form what I have head, Ridley (even though a lot of this fans here aren't so great) seems like a good choice for Brawl.
It's not just any bias, it's logic and reaosning.