All the current games consoles are good and each has its own strengths. It is not a matter of better or worse just more what your requirements are.
1) Nintendo Wii
Strengths - Cheap. Unique controller that is well supported by games that are exclusive to the Wii. Free online service.
Weaknesses - Has less graphic capability and CPU horsepower than its competitors. No DVD playback
2) Xbox 360
Strengths - The core system has now got pretty cheap. Good graphic and CPU power. Xbox Live is an excellent online service.
Weaknesses - Earlier models seemed to have a high rate of hardware failure. Subscription must be purchased for online connection through Xbox Live.
3) Sony PS3
Strengths - Blue Ray disk player. Good graphic and CPU power for games that have been optimized for PS3 hardware. Free online service for online gameplay. Has motion sensor controllers but not as accurate for control as the Wii controller which is optical rather than motion sensitive.
Weaknesses - Sony At Home online community isn't as mature as Xbox Live but it is getting better. It is the most expensive console available.
[This message has been edited by Nigel (edited 11-23-2008).]