They are nearly the same kind of software using in process simulation. If you have known one of them, it is easily to learn the other. In refinery, does not mind which one to start with. The more you use it, the more details you will find. No software is absolutely perfect.
To start, first you need to know what kind of the structure of the software. then it is good to learn the examples in their guide books step by step, which can help you to know how a simple process is simulated, and how it is structured.