Amazing to me how many repliers are still referencing "RPM Hell". RPM Hell hasn't existed for a long time, and yum is speedy and makes installing software as easy as it is under Ubuntu. Anyone who says otherwise hasn't used Fedora in a long, long time. I also tend to think Fedora has better quality packages overall... they have some pretty strict guidelines for how things are packaged up and vetted before being added to the repository (another contributing factor that limits overall size IMO).
Ubuntu does have a larger software repository however -- and don't have as many qualms about including "non-free" software that often can be the key to making things "just work" (video drivers, wifi drivers, etc). Sure there are third party repos for Fedora that do the same, but a user would need to go find them and set them up. Not as integrated.
Fedora itself also tends to be a bit more bleeding edge. This attracts the developers, but might scare away the average joe user who doesn't want to deal with quite as much churn between releases (although Fedora does a great job of QA'ing!).
Just my $0.02. I'm a Fedora user myself...