I currently own a PlayStation, Nintendo 64, PlayStation 2, and a GameCube. I actually just recently purchased the GameCube only for the latest installment in the Legend of Zelda series, Twilight Princess. Hey, call me crazy for buying a system for one game, but I got the system for $25.00 (USD).
As for the latest consoles out there, personally, I wouldn't go buy one just yet. More often than not, they're over-priced and temperamental. The console will most likely die on you and cause you to purchase a replacement before the next generation of systems is released. Therefore, I advise you to wait about a year until the prices drop and all of the consoles are basically as good as they're going to get.
For buying one, it's entirely up to you which one you buy. Each of the three, newest "main" consoles out there (PlayStation 3, Wii, and XBox 360) have their strengths, their weaknesses, but more importantly, they have video game series franchises tied to them. I never kept up with XBox and Microsoft very much (the biggest proprietary money maker they have is Halo, if you ask me), but the Wii has the Legend of Zelda series attached to it, along with Mario and several other prominent video game figures that are generally associated with Nintendo and that you are most likely most familiar with. In my opinion, the PlayStation 3 and Sony produce the best video game series (Final Fantasy, Metal Gear [for some reason I keep thinking there was a Metal Gear installment on GameCube...], Resident Evil [though, again, the GameCube saw some Resident Evil action], and the Grand Theft Auto series [though you may see that on the latest XBox]), but I personally am more attracted to those types of games.
Establish what you want out of a console. This is my general consensus of opinion in the matter (note that I am mostly speaking of past experiences with the three companies [Nintendo, Microsoft, and Sony] and assuming that their past practices carry into the next generation of consoles):
If it's for a good time with friends, more interactive and casual gaming, go with the Wii.
If you want in-depth story games, containing mostly single player action and generally long gameplay hours, look up the PlayStation 3.
If multi-player action with similarly themed games as the PlayStation 3, and with superb visuals, I recommend you try the XBox 360.
A final note is that, though the prices on all three consoles differs independently, the PlayStation 3 is A LOT more expensive than the other two. A lot of opinion I've seen and heard from people is that the Wii will dominate the gaming market this generation. Hey, it eventually comes down to being your call on what kind of experience you want from your games.
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