If Ed Stafford chose to use a Camelbak water bottle, for his epic adventure up the Amazon river, then that's a big enough endorsement for buying one.
I own a Sigg mini flask, which is very high quality, but i am not a convert to aluminium water bottles, so cannot suggest you buy one, but their extremely popular.
Best place to buy one, if you must have a Sigg or equivalent aluminium, is TK Max.
They had a vast selection of Sigg bottles a few weeks ago, in all the designs you could ever want, and none of them cost more than £12.