The more people see and test a set of code, the more likely it is to spot a flaw and fix it quickly.
In general, open source software gets closest to what users want because those users can have a hand in making it so.
Business users can take a piece of open source software and tweak it to suit their needs. Since the code is open, it's simply a matter of modifying it to add the functionality they want.
The visibility of the code behind open source software, however, means you can see for yourself and be confident.