Fresh garlic (Allium sativum L.) is one of the main bulbs cultivated and consumed worldwide as traditional medicinal plants or functional foods. Several biological functions of garlic have been reported and indicated owing to its organosulfur compounds and polyphenols. However, a critical drawback of fresh garlic is its strong odour and pungent taste. Thus, black garlic, an aged processed product, has gained importance as an alternative due to the fact that it possesses a sweet taste and less pungent odor compared with fresh garlic. Previous research has shown that pre-harvest factors like genotype and heat treatment conditions used to produce black garlic are important parameters that affect not only the contents of bioactive compounds but also their nutritional quality and biological properties. This work focused on the evaluation and comparison of the nutritional quality, bioactive compounds (total and individual phenolic compounds), antioxidant activity (by means of the DPPH method), and the correlation among these traits in nine clones of fresh garlic and its aged product, black garlic. For this purpose, nine clones, classified according to ecophysiological groups, were chosen from the germplasm collection of INTA La Consulta. Black garlic was produced in a ripening chamber for 7 days at 80 °C and 30 days at room temperature. The results denoted that the moisture content material of black garlic was reduced, while crude protein, crude fiber, crude ash, and carbohydrate contents were considerably improved. In addition, it was found that black garlic presented a higher total phenolic content (1028.84-1727.95 mg/100 g dw) than fresh garlic (228.49-403.65 mg/100 g dw) and four to nine times more antioxidant activity. Hydroxycinnamic acid derivates were found to be the main phenolic acids in both fresh and black garlic. The antioxidant activity was correlated with polyphenols content and pungency levels. These findings highlight a need for a careful consideration of garlic clones in both dietary and therapeutic contexts.