Indexing vs. Partitioning is not a 'What's better' question because they aim to solve different problems. Indexing is primarily a performance feature while partitioning is primarily a management feature (to make it easier to administer big databases).
However, there is an overlap as partitioning can also improve performance in some use cases—but not in general, just in some cases. Badly partitioned table can also hurt performance—just like badly designed indexes can.
If you'd like an answer that helps you further you'd need to explain your use case in detail.