I **LOVE **my soda machine (it was still called sodaclub when I got it). My family all agrees that the provided flavors are not too good, and the artificial sweetener in it is especially bad.
I mix sparkling water with frozen fruit juice concentrate to make pop/sparklers. Grape, cranberry, mixed fruits, limeade, mango-orange, etc, are all great. Orange juice concentrate is the only one that doesn’t come out very well, in my opinion. Just add the concentrate to taste, usually less than 1/4 concentrate to water. Regular strength fruit juice off the shelves such as black currant is also great diluted with the sparkling water. You don’t seem to need too much juice when it’s sparkling, so even mixed half and half with regular fruit juice, it’s not too diluted.
Out here there’s a brand of adult pop that isn’t very sweet. I don’t remember the name. They serve it at snooty restaurants. Some of their flavors have a mild lemonade flavor with lavender or rosemary added. I’ve made those, and also added mint leaves. Other fresh herbs would be interesting, too.
For a time I made a lot of NY Egg Creams. Sparkling water, chocolate syrup and milk. Those are fun if you can keep the foam from overflowing onto the floor. I found some no-sugar Hershey’s syrup which made it lower calorie.
When I get lemons from Costco, I end up with many more than I can use, so I squeeze them and add some sugar and use it as concentrate for lemon sparklers. The lemon juice is really good with honey instead of sugar, too.
It’s possible to make sparklers out of coffee-flavoring syrups, but I think they taste pretty awful. But if you have any lying around, you could try it.
Seriously, I don’t know why more people don’t get these. They are incredibly economical if you ordinarily buy pop. I don’t, and my kids felt very deprived until I got this. Now they love it.