For me, it was perhaps simple-scan, a very simple and efficient GUI to scan documents. I used it with my Brother printer / scanner and it works like a charm. Especially since I do not scan stuff often, so a program with more complex UI would have the effect that I forget how to use it until the next time.
Out of curiosity, what is it you use it for? I pretty much only use it for SMS, for which it is kinda janky and unstable. Doesn’t always get contact names, doesn’t load everything from conversations, misses messages that I sent or that were sent to me, crashes if I scroll too fast, etc. I have Connect installed just to use SMS (cause I hate typing on my phone keyboard), but I’m honestly not even sure what the base software does.
Sharing files and clipboard is a nice feature. Media control might be pretty neat in some scenarios (party jukebox, htpc).
What completely blows my mind every time is when KDE Connect time pauses my music on my PC when I get a call on my mobile.
Well I basically never use SMS, so I have no idea if they work for me or not.
At the moment I’m using it to connect my two laptops and phone, mostly for notifications, file and clipboard sharing and remote trackpad.
The media integration is great. I can comfortably pause videos I’m watching from my phone’s lock screen. And it does it automatically when a phone call comes in.
And I can use it as a remote mouse and keyboard. That was the first thing I used it for when it was just a small app some guy created for their own needs.
And the clipboard synchronisation is also sometimes useful to get links or so from one device to the other.
If find the missed call notifications to be very helpful. I never remember to check my phone, but I’m on the computer all the time. I also like the ability to remote control the music player from my phone since the computer is hooked up to an amplifier with speakers in multiple rooms.