I use both as well. They server different purposes. When my wife wants to take a quick scan of a paper document and archive it instantly, or have pictures auto-upload, or open and edit a document we worked on a year ago, all on her IPhone, the Nextcloud client works great. When I want to keep the files in my home directory, including some big, regularly changing files, instantly synced between computers and hosted VMs, Syncthing is amazing. I also add Syncthing shares as an external source in Nextcloud, so I can open those files on my phone as well. As others have said, Nextcloud works fine, provided you don’t start installing all sorts of “apps” you don’t need -stick to the basics.