Dear

It's depend on your work what you will do. Please specify which kind of work you want to do.

I asked this question before; the answer was that SAS is better when you have large sample size. However, SPSS can deal with large sample size also. SPSS was design for social science while SAS was design to commercial analysis. in our institution we used both programs. SAS is better for graphs and diaphragms. 

As a conclusion both are good for social and medical science. 

Please see the below conclusion which I copied it from website:

Overall Summary

Each package offers its own unique strengths and weaknesses.  As a whole, SAS, Stata and SPSS form a set of tools that can be used for a wide variety of statistical analyses.  With Stat/Transfer it is very easy to convert data files from one package to another in just a matter of seconds or minutes.  Therefore, there can be quite an advantage to switching from one analysis package to another depending on the nature of your problem.  For example, if you were performing analyses using mixed models you might choose SAS, but if you were doing logistic regression you might choose Stata, and if you were doing analysis of variance you might choose SPSS. If you are frequently performing statistical analyses, we would strongly urge you to consider making each one of these packages part of your toolkit for data analysis.

reference: http://www.ats.ucla.edu/stat/mult_pkg/compare_packages.htm