I just played Wii Fit a couple of days ago.  I thought it was going to be totally stupid.  I was wrong.  It was fun.

My dad bought it.  He needs to use it to stay fit, even though I don't think it would help me stay fit at all.  But the games were pretty fun and it was a good way to get him involved in some thing that I like to do.

Ok I'm going to tell you what I know from experience. 
First of all I own both a PS3(80 GIG) and a Wii(My brother got it) Also I've used my freinds 360 for a month (didn't wanna pay for xbox live)

DISCALIMER:NO SYSTEM IS "BETTER" THAN THE OTHER

The Wii:The only games recommended are games nintendo has made themselves, The Wii store is not helpful for buying any Wii platform games. NGC Games will not work with the Wiimote, and Virtual Console games require virtual controller. This system is at its best when its played multiplayer(Locally) do not let the hype fool you, Online for the most part is a huge complicated mess. Also the controller is more complicated then it seems. The Wiimote requires 2 AA batteries, unless you buy the rechargeable pack, also you have to sync the any new Wiimotes to the Wii via the sync button on the Wii and the Wiimote. The Sensor bar is responsive but its position determines how your Wiimote will point on screen, which for some games is crucial. Expect frequent errors when navigating the Wii store. Also disks go in with the readable underside facing the power button, if your Wii is flat laying down then, you put it in upside down. Finally, The Wii Menu is quick and easy to navigate, but for many games saving is a hassle. Also, the Wii cannot store or play MP3.

Recommended game : Super Smash Bros Brawl ( with GC controller) 

 The PS3: Large Library of very good games, however before you buy any games make sure at least try to play the demo. If you have a ps2 don't get the Ps3 with backwards comparability. PS3 Emulates ps2 games so it will never be as good as on the ps2. Online issues aren't frequent, but depend on your Internet network. Unlike the Wii or 360, the PS3 basically comes with all its software components, however you will need to update the system when you first get it. Any software extras are free of charge. PSN is also free, the quality is much better than the Wii Store and the it is very similar to Xbox live Gold Membership. The wireless is nearly flawless and Sixaxis is responsive, to sync the controller you simply plug it in to the ps3 and press the ps button. That is also how you charge the controller. I've had a ps3 for 3 years and the only error I've had is my Internet disconnecting once. Themes allow you to customize the menu, and the majority of them are free. There are even some websites that allow you to create your own themes, google them. If your feeling adventurous, you can install another os on your PS3. Open source Linux is the easiest way to use our ps3 resources for other things. Its totally legal and does not invalidate your warranty.

Recommended game: Little Big Planet 

The Xbox 360: This is the only console I don't own so don't take my word for it completely. The best games on this system are its FPS games. The Wii's FPS games are not very good, the ps3 fps are on the same level as the 360, but 360 has a larger amount and variety of them. I don't have any exp with the new Xbox marketplace or menu so I won't go into detail about them. The controller is fine but, the battery pack juts out of the back of the controller and makes the controller very bulky. Other than that and the Xbox button in the middle the controller is exactly the same as the old one. It is the loudest system and the quickest to overheat and also has very strict regulations on modding. It is also the only system that uses a disk tray. Because it has no portable system, you cannot access it through that non existent portable system. You can access it through your computer however. Overall, the worst part would be that Xbox Gold Membership, which is about 50$ a month is required to play online games.Also, get the normal 360 the arcade one (the cheaper one) is useless.

Recommended Game: Halo or God of War 

you should most deff get super smash brothers brawl. also mario galaxy, rockband 2, super mario galaxy, metroid prime corruption and thats all i can think of

So have you decided what you are going to get? :P

All of the above are fun.

(Don't buy the DDR game(s) for the Wii, they aren't good)

If you ever plan to buy a decent DDR game, get either DDR X or DDR Max for the PS2. XD 

Other than that, most third party games have little to no value.  They are just trying to ride the Wii's massive popularity knowing that hordes of unsuspecting parents will buy games like "Carnival" and "Minigolf" for $60.

Super Smash Brothers Brawl is an excellent game though, plus it allows you to create your own levels!