The thing with Rock Band and Guitar Hero difficulty is that, as I mentioned, Rock Band aims for realism and GH aims for challenge.
That means Rock Band will have a lot of double notes following each other decently fast, following the actual guitar charts, and generally trying to mimic the actual song's "feel" on the real guitar.
Guitar Hero, on the other hand, will follow Guitar, Bass and sometimes Synth charts in order to keep throwing notes at you, as well as adding more notes than are actually played and difficult triple note combinations. Mostly, though, they'll put zigzagging solos in every spot they can.
Some people might have more trouble with the Rock Band realism and the numerous double notes that keep changing, while others might have trouble with the random triple notes and zigzags in Guitar Hero.
Oddly, while I own a 360 and am really satisfied by it, I'm not a multiplayer person at all. I pay for Live since I do use it every now and then, but what really gets me in a game is the Single Player experience and the emotions and adventure related to it. I much prefer going through a story with jaw-dropping moments, scary moments, badass moments, etc. than playing online for the simple satisfaction of "pwning noobs". Challenge just doesn't hook me in as much.
Nonetheless, the reason I still love the 360 is that while its multiplayer features are currently still the pack leader, its single player software never ceases to amaze me. It's all about the software, really, when it comes to single player. Since I don't like Japanese games (except Nintendo), which make up most of the PS3's main exclusives, I find the 360's game library to be the best for my tastes with stuff like Dead Rising, Gears of War, Assassin's Creed, Mass Effect, Bioshock, Half-Life, Portal, Rock Band, Fable, Halo and Halo Wars, Call of Duty, GTA, Fallout 3, Brothers in Arms, Mirror's Edge, Splinter Cell, Far Cry 2 and so on all being available or exclusive to the system.
In other words, in my mind, the Wii is for Nintendo fans and casual gamers, the PS3 is for fans of Japanese games or people who want Bluray, and the Xbox 360 is for everybody else.
I don't consider myself a fanboy though (just someone whose tastes are better suited to the 360 for the moment), as I'm still planning on buying a PS3 eventually once LittleBigPlanet and Killzone and such are out. In fact, I recommended a PS3 to one of my friends and a Wii to another one. So don't hate me
And finally, regarding the PC, it used to be my main gaming platform, but since the new generation I've changed. Why? Software. PCs are a bit more expensive, and that would have been okay if the game library wasn't greatly inferior in my opinion (except Spore, Blizzard and Valve but those games will run on my Macbook Pro anyway). I don't quite understand how some people still cling blindly to last generation's once true but outdated arguments of console games being dumbed down and all the same. The tables have turned, guys, and although the PC versions of console games are usually better, they do not warrant a 1 year wait! At least that's what I think. I certainly wouldn't, on top of that, pay a premium on hardware for it.