Why are there 2 packages for some applications (e.g. Chromium) in Ubuntu Software?

When I search for Chromium in Ubuntu Software on Ubuntu 16.04, There are 2 options.

Which one should I select?

The same can be observed with VLC media player, Clementine, Inkscape etc.

Solution 1:

The first and the third items are both the Chromium browser. The former is a snap package and the latter is a Debian package.

You can confirm this from the version numbers and descriptions. The first:

matches:

$ snap search chromium
Name      Version       Developer  Notes  Summary
chromium  62.0.3202.75  canonical  -      Chromium web browser, open-source version of Chrome

The second:

matches:

$ apt search chromium-browser
Sorting... Done
Full Text Search... Done
chromium-browser/xenial-updates,xenial-security 62.0.3202.75-0ubuntu0.16.04.1313 amd64
  Chromium web browser, open-source version of Chrome

and the AppStream description:

$ appstreamcli search chromium
Identifier: chromium-browser.desktop [desktop-application]
Name: Chromium Web Browser
Summary: Access the Internet
Package: chromium-browser
Icon: chromium-browser_chromium-browser.png

Using the gnome-software command should help. Both of these commands open the third entry:

gnome-software --details=chromium-browser.desktop
gnome-software --details-pkg=chromium-browser

Here, chromium-browser.desktop is the AppStream ID, and chromium-browser is the package name.