It has been my experience that most ALL of them will produce a gerber. There are not good gerber and bad gerber files. It either is or it is not. So, the differences in the software packages ar chosen by what you like best in the application. User interface, selection of parts, ability to create library parts, support offered by the author, etc.
My personal choice is Eagle. Demo version is at www.cadsoftusa.com or www.cadsoft.de
There are also some others in the download section of this site.
MP