This depends heavily on the type of jobs you are running and what the application you are using supports. It is best to contact the help desk if you need help selecting the best supercomputer for your job. As a rule of thumb:

• Aquila is best suited for sequential jobs that are difficult to parallelize and require large amounts of shared memory (160 Processors, 160GB RAM).
• Hydra is best suited for running jobs that are sequential in nature and only require a single nodes worth of resources (less than 2GB RAM , Up to 2 processors).
• Corvus is best suited to run large MPI based jobs that can run in parallel across multiple nodes. (MPI jobs up to 544 processors and 544GB RAM).