The choice is more complicated than just butyl versus latex, as a range of weights are available for each.
The ultra light butyl Schwalbe, Michelin and Vittoria tubes provide a decent compromise between weight, practicality and price, imho. Schwalbe Extra Light are my favourites at the moment. They're proving reliable.
Continental Supersonic butyl have been ridiculously unreliable, IME. They're so thin that the 700x18-23 version is lighter even than any latex tube at just 50 grams. It only takes a little bit of abrasion for holes to develop.