I'm gonna list the advantages of why Brawl or Halo will do better than the other.
Halo 3
1. launchs before brawl.
2. Is a fps. (most if not all fps do well on 360)
3. A lot of advertising.
4. Better first and multiplayer modes. (not going into details)
Super Smash Bros. Brawl
1. Releases right before christmas.
2. Cheaper
3. Wii will have sold a lot by the time it launches.
4. A lot of new stuff. (not going into details)
Their may be more advantages for both so let me know and I will add them. Hope this helps people decide which will win.
Official member of the Sonic Support Squad! 
Bet with OriGin: Within 1 year Super Smash Bros. Brawl will be ahead of Mario Kart Wii (when aligning the one whole year from each region). 2 week ban from Vgchartz for the loser. Edit: Darn! Looks like OriGin will win. 
