Got to know about OSMC/Kodi last week. Took out my Raspberry Pi. Setup OSMC over the weekend, did all the cable setup for 4 external hard drives and connected to TV via HDMI. After few configurations, I'm all setup. I'm astonished by all the features it provides. Fetching data from TMDb (I had actually created a javaFX app to do this for my local library just last month), remote control from Android as well Web Browser. Enabled UPnP and now I have my complete media center floating around my house network. It is one of the best open source project I have laid my eyes upon. Wish I could attach more pics.

I need advice!

I have a project idea that involves creating a cross platform gui but I cannot decide on a framework.
I have been toying with the idea of electron(ugh please no), c++ with either gtk+ or qt, Java with JavaFx.
I really want to be be able to create binaries for Mac windows and Linux while keeping bundlesize low and efficiency high. With this in mind I am leaning towards a c++ implementation but qt (which seems to be the best option for this route) has an insane learning curve. Is there something I am not thinking of that would satisfy these requirements?

A colleague of mine were bashing all day long about which JavaFX scene builder is the best. Let's settle this what do you think?