TradingView is better for reading; NinjaTrader is better for acting
TradingView usually wins the first impression because it opens fast, is easy to understand and has a huge ecosystem of ideas, scripts and layouts. For exploring markets, comparing symbols and visualizing context, it is hard to beat.
NinjaTrader is not trying to be a social chart platform. It is trying to be a workstation. Once you know what you want to do, its value appears in execution, order handling and the ability to enforce risk rules locally.