@Moon Goat - I'll be honest, I do
like modern UI, I think it's hard to get just right. I think I described this badly, but what I was saying is that these elements matter less than the feedback the user receives when interacting with them, and I can't see any of that from a picture. Reading my comment again it sounds really mean, but I just meant I don't have enough information to say which one is better beyond what colors I like best. Someone posted a menu they did recently .... who was it? It was a nice flat style, but the animation and input feedback was on point, it just looked really good. Let me see if I can dig that up real quick ... here it is, the menu is just the first forty seconds or so.
@DukeSoft's project:
Also, this is Google's material design guidelines
https://material.io/guidelines/.
The point is that a minimal or modern UI is more about the user being able to tell at a glance what is going on, what they can interact with and what they can't. In your pictures, you have the flat down but from this static image it's just too busy. I don't think any of it's bad, it's just all out of context so it's not easy to say 'that looks good'. I would gladly recommend a nice flat visual style with bold, easy-to-recognize information but just keep in mind it's really easy to overdo it and quickly escape the point of being a minimalist UI in the first place. For example, text? Don't use a lot of it. Basically don't make the user read unless they have to, save that for concepts that need explaining. If you do use text, make sure you pick a sharp type face that is nice and legible. Lastly, make sure it's evident what is useful and what isn't. In your first picture the buttons along the bottom seem useful, but it's not obvious if one is selected or not. Here's my edit of your above, this is a lazy edit and I apologize for that but it should explain some of what I mean.
I could keep playing with it but as you can see I've elevated some elements, uncluttered the screen a bit and tried to add some emphasis to whatever is currently being interacted with. I don't know if you'll find this information useful, but if it does, there you go! The only issue with flat design is when everything is flat and then you can't tell anything apart. That said you have the shapes down, and I like the clean lines so run with it and see what you come up with!