After the fall of the Gupta Empire, the northwestern region of India, particularly areas like Punjab and the Indus Valley, became more prominent with the rise of new powers such as the Maitraka dynasty and later the invasions by Central Asian tribes. However, if you're looking for a more thorough answer, the south of India also witnessed the rise of powerful kingdoms like the Chalukyas and the Pallavas during this period. So, while the north saw significant changes, the south also gained power.
If you have to choose one region, it would likely be the north or the south depending on the historical context you're referencing. For the sake of your question and if only one answer can be provided, the south would be a suitable choice due to its significant rise in prominence post-Gupta.