Family Tree Maker is the most popular. I have both it and Family origins for Windows. I like Family Origins for Windows better. It is intuitive to use, has a GREAT custom report utility, and has a great selection pop-up. You can select people - to look at them, to report on them, to export a GEDCOM file - eight ways from Sunday.
Don't delete anything from your Mac before you unplug it, obviously. FOW uploads GEDCOMs easily, if it can read them. Your first try would be telling Reunion to export the GEDCOM to a PC-readable diskette. If the PC can't read it, try exporting the GEDCOM to your hard drive on the Mac, renaming it "xxx.TXT", telling the Mac to export the "text" file to a PC-readable diskette. Read the diskette into your PC as a text file, then rename it back to "xxx.GED".
You could browse the GenForum pages for the various software packages to get an idea of what soert of problems people have with the programs, and how likely someone else is to be able to help them.