I'm completing my PhD in sociology and I've had occasion to use the major statistical packages: SPSS, SAS, R and Stata. Stata is unquestionably the best of the bunch, and for Mac users there is really not even any competition. Some people love R but it's really designed for programmers more than for data analysts.

I recently decided to buy a statistical package for my old Mac Powerbook, and Stata was the clear choice for the following three reasons:

1) Mac friendliness. Look on the SPSS website: you'll be able to buy an out-dated version of the software several versions behind that has been ported to Mac. SAS doesn't offer Mac software at all. R is cross-platform, of course, but I've found the learning curve to be quite steep.

2) Fair price for a VERY complete package. Not only is SPSS expensive, you need to buy extra modules to perform fairly basic analysis like binary logistic regression. I bought intercooled stata for $155 US at a student discount. You can get a one-year license for under $100 dollars. This includes the entire full-featured package with all basic statistics (descriptives, graphics, linear/poisson/logisitic/probit/multinomial regressions) plus modules for time-series, event history, data reduction, panel data, survey statistics, pretty much everything. There are four different types of stata - Small, Intercooled, SE, and MP - but unless you're dealing with datasets with more than 2,000 variables, intercooled is a good affordable option.

3) Quasi-open-source structure. You can search for user-created add-on modules within the program and install them automatically. Suppose you need to simulate data for a Box-Jenkins ARIMA model - just search and you'll find someone has added a module to do just that, so you don't need to write it yourself. The help is also excellent, although as some people have noted the large and expensive manuals would sometimes be nice to have. However, the program comes with a 150-page "getting started in Stata" book that is excellent and mac-specific.

As far as I can tell, Stata 10 is quite a bit better than 9. The improvements in graphics editing alone are really noteworthy.

Side note: Stata integrates very nicely with TextWrangler and Smultron; both feature text highlighting for stata .do files.

Very highly recommended for anyone needing a complete statistical package.