Do you mean for simulation of chemical processes/heat and material balances? Or do you mean for design of the physical equipment?
In either case, you must consider what is meant by "best." Often that is a matter of "best for whom" and "best for what purpose." In the case of process simulation, there is no one program that is best for all engineers for all purposes, despite claims of the vendors to the contrary. You must consider how you will use the software and what your needs are. HTH