The PS3 and 360 are pretty much comparable in terms of power. The Wii is somewhat more powerful than the original Xbox, but not even close to the class of the other two. (This is why it's so much cheaper)
The PS3's real difference is that it comes with a Blu Ray drive. Which might also be its weakness. (since it drove up the cost, and is a bit slower than the DVD drive in the 360, although you apparently install games to the hard drive, to offset this, or the most important bits anyway). I'm also not sure the PS3 is powerful enough (its GPU is about on par with a Nvidia 7800, already obsolete) or has enough memory to take advantage of the added space Blu Ray gives. Some games, like Virtua Tennis, do supposedly have more detailed textures than their 360 counterparts, but most are pretty much the same
As to games, I really think you'll see that most big name games by 3rd parties will go to both the 360 and PS3, unless funded by either Sony or MS. Because development costs are so high.
Right now, Oblivion is only on the 360, but will be on the PS3 in 1Q 2007 (supposed to be a launch title, but moved back apparently to add microtransaction support). Because it's simply not very powerful, you won't see that on the Wii, but they might do something like it if it catches on (the PSP is getting an Oblivion title, the Wii might get a port of that, or something like that). The Wii will have Zelda, though.
Anyway, if you like Western RPGs, then 360 will probably be the best bet. It will also have Mass Effect, which is a sci-fi shooter/rpg combo from Bioware. And MS has financed some fairly impressive japanese RPGs (Blue Dragon and something)
I really wouldn't expect many strategy games on either console. At least not like Total War or Civilization. The 360 will probably get some RTSs (Battle of Middle Earth sold well) and there's the upcoming Halo Wars, and the PS3 will likely get some Romance of the 3 Kingdom games.
The 360 probably wins out in the shooter department (assuming you mean FPS). Halo 3, Gears of War, The PS3 does have Resistance: Fall of Man which looks interesting, but likely not in the class of either GoW or Halo.
Since they are so expensive, I'll probably end up just getting one console (usually I would get them all when they hit $200), and I'm probably going to get the PS3, because it will likely have more Japanese RPGs (which I like).
And oh yeah, both the 360 and PS3 should be getting the supposed Oblivion killer from EA. Not much is known about it, except it's set in Middle Earth, and uses Sims 2 AI, and called "The White Council".
http://en.wikipedia.org/wiki/The_Lord_of_the_Rings:_The_White_Council