The lower end stuff is crap, and will drive you mad over time. This includes X-10, Insteon, and UPB. These products will fail. It's just a question of how long before they do. Z-Wave is a technology, not a product line.
If you want something complete and reliable, go for Lutron RadioRA. Version 2 of this industry-standard system was released recently, and prices have become more reasonable. This is a whole-house solution. They also offer single-room and smaller-scene packages, and the mother-load solution called HomeWorks, which pretty much rules out retrofitting.
http://www.lutron.com
Note that you'll want a pro to install and configure these switches, unless you're really geeky and comfortable with handling electricity. And single.
Edit: Here is a link to a discussion about this very thing on a pro site. Read the comments:
http://www.cepro.com/article/hardwired_vs_wireless_lighting_control/