By using the word "accurate", are you meaning "realistic"? I think that all of the major software analysis packages are "accurate" (i.e.: precise). If you are rather asking about realistic answers, then you only get out of a model what you put into it. Better modeling with better assumptions made by you will provide better, and more realistic, answers. Use the software package that you like, and feel most comfortable with, and use good judgement in making the assumptions required by any good model, and you will get realistic answers in return.
Dave
Thaidavid