Kombucha is a fermented tea beverage produced by a symbiotic culture of bacteria and yeast (SCOBY). The quality of the Kombucha beverage depends not only on the fermentation parameters, but also on the type of raw materials used, as well as the SCOBY starter culture. The aim of this study was to evaluate various types of Kombucha beverages in terms of their microbiological quality, including antibacterial properties and physicochemical characteristics. Two different SCOBYs—Italian and Polish—and three variants for each starter (tea-based, milk-based, and rice-based Kombucha) were used for fermentation. Microbial counts (CFU/mL), antibacterial activity, and chemical analyses were performed over three days. The results showed stable fermentation across all substrates, with microbial counts increasing from ~0–2 log CFU/mL at Day 0 to ~3–12 log CFU/mL at Day 3, depending on the matrix. A pH reduction of ~1.1–1.3 fold confirmed active microbial metabolism. Antibacterial activity was highest in tea-based Kombucha, with inhibition zones of up to 17 mm against Staphylococcus aureus and Escherichia coli, particularly in beverages fermented with the Italian SCOBY. These findings demonstrate the adaptability of Kombucha fermentation to different substrates and contribute to expanding knowledge on the potential production of functional beverages using alternative raw materials.