In general, you should download the 64-bit version of MATLAB if your computer has a 64-bit processor and a 64-bit operating system. According to the MathWorks roadmap, they are moving away from 32-bit support on most platforms.
The 32-bit ("maci") version of MATLAB will not be updated after R2010a. All future versions of MATLAB require a 64-bit processor. For information about your processor, choose "About This Mac" from the Apple menu.
All Intel Macintosh computers have a 64-bit processor except:
- Intel Core Duo (not the same as "Core 2 Duo")
- Intel Core Solo