Sigg has been making water bottles since 1908, so I figure they have had some time to perfect things. The fact that they use epoxy coated aluminum bottles has recently caught a lot of attention since some studies have show that plastic Nalgene bottles can leach harmful chemicals. That means the Sigg bottles are safer to drink out of. Personally I can tell a difference in the taste too, especially after having orange juice in the Sigg for the day, when you wash it out the water tastes like water, not orange water. Perhaps what I like the best about Sigg is their good eye for design. The two bottles shown above are my wife's and mine. The blue (mine) is a soft touch baby blue, which has a nice powder coated type of paint job. Matte and sexy. My wife has the nice orange graphic print on hers. Both have a nice active bottle top, which means the water only comes out when you need it. No hands needed.
Sigg also has some really nice small insulated mugs, which I haven't been able to get my hands on yet, but if I do, I'll be sure to do a write up on them. They are really beautiful.
Check the Sigg home page on sources where to buy.