honnestly with more than 6 years working with Petrel and about 5 years with RMS I would prefere RMS rather than PETREL ( due to some option in gridiing and fault definition (QC)) , also due to the easy way to export the workflow to another project which can save time. but it also depend of the Fluid that you are trying to model... if it s gas or light oil .... it doesn t matter which software you use .. even a spreadsheet or material balance will be sufficient