A good platform will be E*Trade as it is filled with educational resources such a videos, articals and webinars. You will stay up to date with investing news as well as reports with the aid of analystics on key areas. This platform is best for beginners.
If you want to trade stocks on your own, use ameritrade.
If you just want mutual funds, you can stick with vanguard
Highly recommend Robinhood which is available on desktop and iOS. It also has free brokerage.
Alternatively keep an eye out for Revolut as they're an EU unicorn about to come to US, Asia, and Australia shaking up banking, investments, and even cryptocurrency.
I personally use Vanguard and the Robinhood app. Both great platforms to start trading on. I really loved robinhood due to the free trades.