The amount of seltzer I consume makes price and fizz lasting both important factors. If possible please include price in posts.
I found that the 24 pack of deer park bottles they have at Costco for $6.99 (at least in OH) is the best. Comes with 6 lemon, 6 orange, 6 black cherry and 6 raspberry lime. Works out to 29 cents a bottle half the size of the Adirondack/Beer Mayim. Fizz rarely runs out. A distant second (Costco sometimes runs out) would be...
In my experience, Adirondack seltzer is the very best in flavored seltzer. Mammesh tastes like soda just without the sugar.
My kid actually likes it just as much as he enjoys soda.
At Marc's they are about 60 cents each.