Aspen Plus evolved as a chemical process simulator - it is very strong for simulating non-ideal properties, systems with electrolytes, solids, azeotropes, and chemical reactions. It is also strong for modelling large-scale flow sheets (using the equation-oriented approach).
Hysys is optimized for upstream oil & gas, gas processing, and refining applications.Aspen HYSYS has more in-depth utilities. It has better support for things like Assays and has built in Power Plant refinery reactors, like FCC's and catalytic reformers. It has a good workflow cantered around 'forward-backward' solving based. Hysys is the most user-friendly process simulator. But again, it depends on how much time one has spent working with any software. The process is also suitable for optimization in GT power plant. You must be chosen higher version to compare their model results. It is easier than ever to confidently upgrade software versions without the risk of hindering existing projects. In today’s highly competitive market, you don’t have a lot of time to spend deciding when to deploy the latest software; with the Aspen Version Comparison Assistant, you can do it in minutes.