I have wondered for a while whether it makes a difference with health or eco concerns which water bottle is better, glass or stainless steel?  Turns out if you are just drinking straight water, you are probably good to go with either one, and both are safer than plastic.  These are the differences I found:

Glass does not leach into food or liquids, however, the drawback is that it breaks.  The good news is there are some cool new options for glass water bottles, where you should be pretty safe from breaking.  Lifefactory glass water bottles have a silicon (silicon is natural and non-toxic) water sleeve which helps with the falls.  The other plus is that you can put any food or drink (coffee, tea, juice, soups, etc) in this bottle and will have no leaching problems. You can see how much water you have in the bottle and are drinking, and I personally like the taste of water better out of glass.

Stainless Steel seems to still quite safe with water, though it may have leaching issues (such as iron, chromium and nickel) depending on the acidity/ph of the item, as well as other possible factors, in which it comes in contact.  If you have plans to use the bottle for anything other than water, you may want to consider going with glass. I could go on an extremely long dissertation about this, but there is an excellent explanation found at the following link if you would like to read comprehensive detail: http://www.debralynndadd.com/_blog/greenlivingqa/post/Stainless_Steel_Leaching_into_Food_and_Beverages, which sums up a number of things I read. The benefit of stainless steel is that it obviously does not break like glass, and there seem to be more friendly drinking bottle options, especially for kids.  I never really loved the taste of the water out of stainless steel, but for the sake of avoiding plastic, it is still better, and there are some bottles that have attached water filtration systems that you can buy with them.

We are going to buy some new glass water bottles tomorrow for my family.  I believe I saw Lifefactory bottles at Target, and if they are not found there, they can be purchased online at ReUseIt.com (9 oz, 16 oz or 22 oz).