Plank is the default dock in elementary OS as well as a the underlying tech behind the Docky dock. Plank is a bare bones dock for those looking for something simple to launch applications.
Ranked in these QuestionsQuestion Ranking
Pro Solid and lightweight
Pro Simple and minimal
Plank is a good choice for those looking for something simple that just does its job well. There is no UI for options built in to the dock as to change anything those options will have to be accessed through a text file.
Pro Third party themer available
An additional third party app has been developed that allows theming the dock without the use of any extra resources. This is great for those that are not using elementary OS and the elementary tweaks extra.
Con No right click menu for some apps outside of elementary OS
Other file explorers and terminals (those not found in the default elementary OS) do not have any right click menus for the dock meaning it is impossible to launch multiple windows for certain file explorers or terminals.
Con Poor workplace awareness (cycling windows)
When configured to only show apps on current workspace, cycling an app open on multiple workspaces will switch workspace focus, update the dock and often leave you to cycle another app.