Partitions and Indexes, in which cases should be used
Easy: you should always use indexes.

Partitioning for performance is probably the most misunderstood myth out there. When you partition, the best you can hope for is on-par performance with a non-partitioned table. And yes, that is including partition elimination enhancements. Reducing table scans to partition scans because of missing indexes is simply not the answer. Replacing table scans with index seeks or index range scans it is a much better the answer.

Partitioning is a great feature for data maintenance and administration and for efficient ETL switch-in and switch-out operations. For a good discussion of pros and cons of partitioning, see How To Decide if You Should Use Table Partitioning.