Selecting a good tile server is very important, as the tile server provides the images that comprise the map your features will be placed on. Tile servers are optimized for both quality and performance, and therefore are superior to simply uploading basemap images.
You can select the default tile server to use from the plugin configuration, which you can then modify for any given tour. Unfortunately, the plugin currently does not support including multiple tile servers within the same tour, so you can only select one per tour.
Remember that the tile server is visual only - nothing will be presented to assistive technology, so make sure no meaningful content is provided solely by the tile server.
This plugin uses the Leaflet extension Leaflet Providers, which includes a rather long list of tile server options. Theoretically all of the options should be free to use, though some may come with restrictions. A small selection of these servers is included in the Select a Tile Server dropdown.
If you want to use a server not listed in the dropdown, you can set the dropdown to Other Leaflet Provider. You will than need to provide the name of the tile server in the field labeled Name of Leaflet Provider Tile Server. You can find a full list of included tile servers (with examples) on the Leaflet Providers Demo. The name to use is directly underneath Provider names for leaflet-providers.js.
Some of the tile servers also have additional requirements for use. Make sure to check the Leaflet Providers page (linked above) for a list of all providers requiring registration.
Two additional relevant text fields are provided on the plugin and tour configuration pages:
In all cases, look to the Leaflet Provider documentation for details on what a given tile server will need.
Note that you do not need to fill out Custom Tile Server Attribution if you are using a tile server from Leaflet Providers. The correct attribution will automatically be used, so leave this field blank unless you really want to overwrite that attribution.
If you don't like any of the options from Leaflet Providers, you can always specify a tile server manually. To do this, select Custom for the tile server and fill out Custom Tile Server URL with the correct URL. You will also almost certainly want to fill out Custom Tile Server Attribution with whatever attribution the tile server you chose requires. The field will accept HTML, markdown, and plain text content.
All other settings (like ID or Variant) are ignored for custom tile servers.