LOL I can't tell you how many times I would get into that fight with a buddy of mine when it came to the N64 vs. his PC. Old times.
Without further ado however, it really depends on what you're looking for in terms of games. As was said if you're looking for games that are focused more on graphics then you should lean toward the PS3 since it uses Blu-Ray format the PS3 is able to produce the best hi-def graphics of the 3 systems. (better than the 360 for sure) You also can get online playability for free unlike the 360 but where the PS3 loses out on the other systems is the fact that, like it's predecessors, the majority of the games are 1-2 players tops in terms of local (same system/split screen) play. There are some games that are for more than two but those are usually related to sports or racing games. So if you're looking for offline playability and game selection then the PS3 is not for you. The kicker for the PS3, as the Mexican Barrister has alluded to, is the fact that it has a Blu-Ray player and that Blu-Ray player in the PS3 is the easiest to update of any player on the market. (Makes sense right, given that Sony INVENTED "Blu-Ray") It adds an overall entertainment value beyond gaming that neither the 360 or Wii can match.
The Xbox 360 is a system that has a bitchton of titles to choose from, above beyond titles that span all systems, and it has a very wide array of games for all ages that you can download from Xbox LIVE (online) for a fee. For a price, you can add Xbox LIVE Gold which is the membership that allows you to play vs other players via Xbox LIVE and that online play is the strength of Xbox along with the title selection. The other thing that Xbox now has is the Kinect sensor which is an addition to the system that uses a camera plus motion sensor array to detect your own body movements and incorporate those movements into gameplay: not revolutionary given the Wii's controls but the fact that you don't need to shell out for a controller is peachy. The major downsides to the Xbox lie in that great number of games but more importantly the price tag. If wanting to get the ultimate experience for Xbox (system, Kinect, Xbox LIVE Gold, extra controller, points to purchase online games and actual disc games) be prepared to shell out 600-700 dollars. Even if you're going with the base experience you're still looking at about 300-400 dollars. The other issue is that there are so many games on the Xbox 360 that they no longer have a truly unique title to call their own (neither does PS3) by which I mean they all play, seem and feel the same. If you're looking for a greater amount of games and the best online play, regardless of price, then the 360 is the direction to take.
With the Wii you're getting not just the system that first introduced overall motion sensor play but a gateway to the past through the Wii's Virtual Console. The Virtual Console is an online Nintendo store where you can purchase Nintendo games for the older systems (NES, SNES, N64, Virtual Boy and a host of SEGA systems) to play on the Wii as well the Wii can play your Gamecube games. (Xbox 360 and PS3 can play predecessor games to a point, many of which need a patch to be uploaded to the system in order for the game to be recognized) The Wii is also, by far, the least expensive system overall when it comes to getting the best possible experience - shelling about 350-450 dollars gets you exactly what you need. Nintendo has made it's mark over the years for introducing titles with such phenomenal gameplay that they are established as the bars for that genre. The one thing that may be construed as a con for Nintendo is that it is not as adult-oriented as the PS3 and Xbox 360 and with a growing number of paying gamers reaching adulthood, it would seem that Nintendo is lacking in that regard. In my belief, and through what I've read, Nintendo has been very comfortable aligning itself with it's target audience - children and their parents, and while they have come out with some more adult-oriented titles, it is not their focus and they've accepted that - they're still making boatloads of money and continuing to be a major flagship in the gaming world so why change? The Wii lacks that "overall entertainment value" the PS3 has but, if your focus is gaming, and you want a wide array of titles for all ages that are fun to play by yourself or with friends, the chance to play older titles you haven't played since you were a kid and most importantly, the best bang for your buck in regards to gaming, then the Wii is where you should go.
What you need to do is to determine what is the most important to you in terms of buying a game system: is it the extras, is it the games, is it the pedigree established, etc. Once you determine what your base needs are and what you're looking to spend then getting a system is a snap. I hope this helps in anyway.
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