Both have their cons and pros, it's always down to which one suits your needs the most. If you want great games, online functionality, multimedia capabilities and secksay graphics, then buy the PS3 or the Xbox 360.
If you like something that is more casual, family friendly, elderly friendly and cheap, the Wii is great.
Done and done. It's always useless bickering over which console is better because they all offer different things. Some may be similar, but they'll always have some things that are superior to each other.