I posted this in the Spidey forum thread. But...
WEll I've now beaten it on 360 and Wii.
My opinion is they both cover the other's flaws but neither is a great game in its own right.
What 360 did better:
It looked better and had more content. Well that's not entirely true. It had about 1.5-2 hours more worth of gameplay. It had the equivalent of 3 more bosses than Wii, albeit Wii had 2 bosses not appearing in 360's, including a great Morbious fight. 360's new bosses included Kingpin, who was a pain in the ass, personally. But Scorpion was really cool to see used again.
With that said it is a beautiful game and really is NEXT-GEN with the goregous graphics. That is a huge bonus so if you buy a gam e only for looks this is the easiest choice (unless you have a PS3, which I don't). Also getting to temporarily play as New Goblin is cool and missing in Wii.
What the Wii version did better:
It was overall just more fun to play. This is the first swinging system that really brings home playing as Spidey. While I think SM2's game swinging (once you've mastered it) is the most percise and freeing to use, this one just feels more natural and while not quite as accurate, it feels more satisfying and real. Using the nunchuck and wiimote to swing is the only thing brilliant in either incarnation IMO. The other thing I really like about this version is the fighting mechanics. 360's is a boring button masher but while it is mostly copying the sword system from Twilight Princess, the fighting works and the use of dodging on spider-sense with the nunchuck feels more natural as does using both hand movements for powerful attacks. And the web-attacks are just much better, especially rodeo-ing and slamming them into the pavement.
City-scape wise it is an ugly mess though. While bigger and more accurate to size than SM2 none of the landmarks are here other than the Empire State Building and the MetLife building. And it isn't as fun to jump off them as in SM2 (same goes for 360 version there too, though). The lack of Times Square is appalling and while the character models are quite good in actuallity the environments suck. On the other hand the gangs are done much better, instead of being counted as cheap "storylines," when they are not, they are a constant threat to the city and can start wars with the police and you are constantly guaging and trying to keep gang violence levels down, which is a cool system. As is the robust RPG that isn't as complex on 360.
The boss fights are also better in that they are fun to play. But dman can they be glitchy. This game is much glitcher than the 360 version which isn't exactly the image of smooth running. And lastly on top of the swinging and fighting mechanics though, the one thing the Wii version really has over the 360 version is getting to wear the black suit whenever you want. Soon as you get it, it is there for you to switch to whenever you want. And it is fun as **** to use, but the price is if you wear it too long you go crazy and black out so you have to time it. But to take it off you have to play a minigame that gets harder each time at literally moving the wiimote and nunchuck in a ripping motion as you try and rip it off. Also an interesting system is the more you wear it the more violent and dangerous NYC gets and the clouds get grey and ominious and trash builds up in the streets. It is a great system which I WOULD HAVE LOVED TO HAVE SEEN IN NEXT-GEN GLORY ON 360 and really should have been used on that version.
With that said Wii is still a glitchy game that is ugly to look at at times and ultimately is only 10-11 hours of gameplay while I can get 12-13 out of 360. So it really is preference. Slightly more content and better graphics on 360. But Wii is actually fun to play particularly when swinging, using web attacks and the black suit combat system which weakens your RPG build up but when used is awesome (and a ***** of a minigame to get off before it kills you).
I rank them the same, 6.5, but I think I preferred the Wii version. I think both are good rentals as for purchases, you need to be a big Spidey fan, which I am.