to be perfectly honest im leaning towards the fact that the Wii will definatly have the upper hand. But from what ive seen at my work and talked to customers about, the majority of them anyway seem to be graphics whores for the most part, or into more adult themed gaming (see gears of war). Im thinking that will be the only downfall of the Wii. Now although they cant get past the fact of not having much eye candy i think its crucial for them to break this mould of catering towards more family oriented games and start to shake it up a little.
for example, look at Resident Evil 4 for the gamecube. Anyone who has played this game knows how much ass it kicked. It was a different spin on the survival horror genre and it worked extremely well. It even looked damn good on the system too. I'm not saying that Nintendo should start pulling out Grand Theft Auto games or things of the sort, im just saying that perhaps by catering towards more mature themed games, they would be able to keep a broader audience.
I would totally love to see Nintendo come out on top, but im just not sure if its going to have the thunder to keep gamers interested for the consoles 4 to 6 year life cycle.