There is a little difference between the two sentences: the first phrase is colloquially used when who talks is glad to drink (we would like to drink it, and so we are glad to drink it – positive sentence), the other phrase is used as a proof of something or to confirm that who talks himself drinks the beverage (Is it good to drink it? Of course, we ourselves drink it).
Examples:
(1)
- Questo vino è buono, ne diamo un po' a Mario?
– No! Ce lo beviamo (tutto) noi!
(2)
- Questo vino, è buono?
- Sì, lo beviamo noi stessi!