[Eclipse]

When it comes right down to it, the answer is there's far less of a difference anymore than people want you to believe. Most of them all play the same games with a few exclusives, and even the exclusives are largely the same experience (hello era of the FPS, no pulling the camera back of few feet does not significantly alter the game). The companies like the flame wars because it generates brand loyalty, but in the end it really, really doesn't matter that much:

PC - A few unique genres you won't find anywhere else. RTS games, MMOs, and other sims thrive here. Extremely precise controls for FPSs (I consider it a little too precise personally) as well. Downside is that most people don't have as good of an audio/video setup for their PC as they would for a console. The mouse and keyboard which drives the unique genres of the PC doesn't work nearly as well on the couch as a controller either.

Xbox 360 - Strong online network with a lot of great community tools. Best if you build a good friends list as the untamed larger internet is the usual cesspool. Quite a few strong exclusive (semi exclusive, they tend to also show up on the PC) games, including several games that may appear elsewhere, but were VERY poorly ported (Bayonetta). Terrific Xbox Live Arcade games. My favorite controller for 3D games by a long shot.

PS3 - Terrific Blu-Ray player. Far superior D-Pad to anything else for fighting games and 2D platformers. Uncharted. Terrible triggers on the controller that was great 15 years ago, but really needs to be redesigned.

Wii - Very different from the rest. Generally a totally different selection of games, even among those that share the same title. Quite a few excellent exclusives that tend to harken back to an older school of game design (ie color, simple controls, fewer space marines). Library bogged down with an absurd amount of terrible shovelware.

As for portable gaming machines... those are an entirely different experience. Hard to compare, but basically, I find the PSP to be useless junk, the DS to be the king of the roost, and the iPhone/Android/phone stuff to be full of absolutely fantastic 3 minute time wasters, but lacking in anything with long term appeal.