Create list in App web or in host web?
- List in App web can be created
declaratively in designer and if you need another changes you can
change the XML itself.
- List in App web is not visible to a user in Site contents and lies at different url
- When the App is deleted, everything in App web is also deleted (all App web can be restored from Recycle bin)
- You should not change settings of a list in App web because it can be overriden in newer version of App
So it's really up to you where you will host the list.
Here you can find nice and simple example of SharePoint-hosted Add-In with list provisioning inside App web https://msdn.microsoft.com/en-us/library/office/fp142379.aspx
Here is example of creating list with column in a host web.
using (ClientContext cc = new ClientContext(auth.Url))
cc.Credentials = new SharePointOnlineCredentials(auth.UserName, auth.Password);
ListCreationInformation listInfo = new ListCreationInformation();
listInfo.Title = "Shared documents";
listInfo.Url = "SharedDocuments";
listInfo.TemplateType = 101;
List newlist = cc.Web.Lists.Add(listInfo);
newlist.Fields.AddFieldAsXml("<Field Name='Column' DisplayName='Column name' Type='Text' />", addToDefaultView: true, options: AddFieldOptions.AddFieldInternalNameHint);