Which stock broker app or the best in terms of functionality and features?

I really like FSM ONE personally for my stocks and Gemini Active Trader view for my crypto.!

I think TD Ameritrade's desktop app is not bad in terms of functionality. It has quite decent charting features and the desktop app has a pretty easy and customisable interface as well.

But personally, I use Tradingview to do charting. For a free site, it does come with quite a wide range of indicators (and even better if you can use their inbuilt code to write your own indicators!).