Ansys Employee

If you have licences you can run multiple Fluent jobs on a single machine. CPU is one aspect, then you've got RAM. However, the cpu interconnect is also important as you need to be able to pass data quickly between the cores on a single chip and between chips/boxes on a larger system. 

"Best" is very dependent on exactly what you're wanting to do, how big a model you have and how many licences you can use.