When comparing Dash to Dock vs DockbarX, the Slant community recommends DockbarX for most people. In the question“What are the best docks for Linux?” DockbarX is ranked 5th while Dash to Dock is ranked 6th. The most important reason people chose DockbarX is:
DockbarX has an available plugin called "DockBarX Xfce4 Panel plugin" that allows DockbarX to blend in seamlessly with the XFCE4 panel, which is great for XFCE users due to the limited options of the default panel.
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Pros
Pro Integrates with GNOME
Dash to Dock is a GNOME extension, so it works on GNOME.
Pro Great plugin to help blend in to XFCE4 panel
DockbarX has an available plugin called "DockBarX Xfce4 Panel plugin" that allows DockbarX to blend in seamlessly with the XFCE4 panel, which is great for XFCE users due to the limited options of the default panel.
Pro Easily customized
DockbarX has inbuilt settings that allow the user to easily customize the look of the dock, from changing the text color to the background color.
Pro Easily the best Win 7 taskbar functionality
If you want a combined launcher/manager, a la Win 7, this is it.
Cons
Con GNOME only
Con Not actively updated
Less than a dozen updates since 2014: https://github.com/M7S/dockbarx/commits/master