I'm coming from NetBeans and evaluating others and more flexible IDEs supporting more languages (i.e. Python) than just php and related.
I kept an eye on Eclipse that seems to be the best choice; at the time I was not able to find an easy solution to keep the original project on my machine and automatically send / syncronize the files on the remove server via sftp.
All solutions seems to be outdated or stupid (like mounting a smb partition or manually send the file via an ftp client!
I'm not going to believe that an IDE like Eclipse doesn't have a smart solution of what I consider a basic feature of an IDE, so I think I missed something... On Eclipse forums I've seen the same question asked lots of time but without any answer!
Some suggestions about is strongly apreciated otherwise I think the only solution is stick on one IDE each language I use that seem to be incredible on 2018.
I'm developing on MacOS and the most interesting solution (kDevelop) fails on building with MacPorts.
Thank you very much.
RSE is a very poor solution, as you noted it's a one-shot sync and is useless if you want to develop locally and only deploy occasionally. For many years I used the Aptana Studio suite of plugins which included excellent upload/sync tools for individual files or whole projects, let you diff everything against a remote file structure over SFTP when you wanted and exclude whatever you wanted.
Unfortunately, Aptana is no longer supported and causes some major problems in Eclipse Neon and later. Specifically, its editors are completely broken, and they override the native Eclipse editors, opening new windows that are blank with no title. However, it is still by far the best solution for casual SFTP deployment...there is literally nothing else even close. With some work it is possible to install Aptana and get use of its publishing tools while preventing it from destroying the rest of your workspace.

Install Aptana from the marketplace.
Go to Window > Preferences > Install/Update, then click "Uninstall or update".
Uninstall everything to do with Aptana except for Aptana Studio 3 Core and the Aptana SecureFTP Library inside that.

This gets rid of most, but not all of Aptana's editors, and the worst one is the HTML editor which creates a second HTML content type in Eclipse that cannot be removed and causes all kinds of chaos. But there is a workaround. 

Exit Eclipse. Go into the eclipse/plugins/ directory and remove all plugins beginning with com.aptana.editor.* EXCEPT FOR THE FOLLOWING which seem to be required:
com.aptana.editor.common.override_1.0.0.1351531287.jar
com.aptana.editor.common_3.0.3.1400201987.jar
com.aptana.editor.diff_3.0.0.1365788962.jar
com.aptana.editor.dtd_3.0.0.1354746625.jar
com.aptana.editor.epl_3.0.0.1398883419.jar
com.aptana.editor.erb_3.0.3.1380237252.jar
com.aptana.editor.findbar_3.0.0.jar
com.aptana.editor.idl_3.0.0.1365788962.jar
com.aptana.editor.text_3.0.0.1339173764.jar
Go back into Eclipse. Right-clicking a project folder should now expose a 'Publish' option that lets you run Aptana's deployment wizard and sync to a remote filesystem over SFTP.

Hope this helps...took me hours of trial and error, but finally everything works. For the record I am using Neon, not Oxygen, so I can't say definitively whether it will work in later versions.
Eclipse Oxygen: How to automatically upload php files on remote server