You can make your sodas as sweet (or not) as you like, and use fresh, natural ingredients. It's no shock that I turn to seasonal produce when making homemade soda (see recipes below).
There are basically two ways to make a homemade soda. The first way involves making a flavored sugar syrup — such as mint syrup, lemon syrup, or ginger syrup — and simply mixing that syrup with club soda, seltzer water, or sparkling water, as in this Lemon Rosemary Soda. These sodas most closely resemble commercial sodas since they are, in the end, simply sweetened and flavored soda water.
The second way to make homemade soda involves muddling, or crushing, fresh fruit and/or herbs along with a bit of sweetener (sugar, simple syrup, agave nectar, or honey), and perhaps some lemon or lime juice together before adding in the soda to mix, as in this Cucumber Mint Soda or Strawberry Soda. These sodas tend to have a lighter feel and a more cocktail-like appearance and appeal than sodas made with a flavored syrup.