Black Ops 2 will sell better, obviously. It's on at least four different consoles. Hell, ever since Modern Warfare 2 the series has been more popular than Halo on xbox alone.

I don't even know what you mean by fanbase.... I guess I'd argue Halo has a better fanbase since theres just more creativity there and theres some actual lore to Halo so theres more than just multiplayer bros... If you mean fan count though then CoD is the obvious winner

Players online and sales basically go hand in hand.

Black Ops will probably be advertised more, but they'll both be advertised the hell out of.

And both will be hyped to heaven and back, but again, Black Ops is on more platforms ...

This really isn't a very interesting debate. There's an obvious winner in pretty much all categories. All I can add is that Halo 4 will probably score better. The Halo series hasn't been as run dry. The campaign looks awesome, the graphics look like a big step up and while the changes in multiplayer might not please all the vets at least they're making alot of changes instead of pushing out the same game as last year.