I mostly really like Flutter. I haven't done a huge amount of UI development work in my life, but of the things I have used, I have found Flutter to be far and

I mostly really like Flutter. I haven't done a huge amount of UI development work in my life, but of the things I have used, I have found Flutter to be far and away the easiest to quickly express the UI you want to build and just build it. I think its killer features are the cross-platform support by default and the hot-reload—I found the hot-reload functionality so invaluable that I ended up jerry-rigging hot-reload into my current product at work. You're right that it is definitely still rough in some places though. The libraries on pub.dev can be very hit-or-miss, and I definitely wasted some time trying various libraries from there before either giving up or rolling my functionality. I too explored a mapping project using it a year or two ago now and ended up having to essentially create my own map view using mapbox APIs (unfortunately I don't have code that I can share from that project). That said, I find Flutter is at least relatively easy enough to implement things that you can't find from the ecosystem.