There is not one "correct" answer to this question, as the relative value of each contribution of the Maurya and Gupta empires is a matter of opinion, and the ranking is subjective. Therefore, this answer should be considered an example. The main purpose of the question is to properly justify your opinion.
I think that the best ranking of the innovations from most important to least is:
1. Gupta number system: The Gupta number system is likely to be the most important development of these empires. This is because the number system was the basis for the Hindu-Arabic numeral system. In turn, this is the basis of our current decimal system. Therefore, it had a lasting historical impact.
2. Mauryan Rock Edicts: The Rock Edicts were law codes that were displayed in public places. These were important because they ensured that the rule of law was maintained. A lawful society is better organized and more peaceful, which allows it to reach a higher level of development.
3. Mauryan tax code: Taxes allowed the Mauryan empire to complete many projects that benefited society, such as roads, waterways and canals. They also increased the power of the government and the empire.
4. Gupta hospitals: While hospitals were a very important development, they mostly benefitted the individual, and did not play such an important role in the culture at large.