What is the best free trading app?

Can you tell me, what would you consider to be the best free trading app available in the market today? With so many options out there, it's hard to decide which one offers the most comprehensive features, user-friendly interface, and reliable security measures. Is there a particular app that stands out in terms of its performance, versatility, and accessibility? I'm particularly interested in one that allows for seamless trading of cryptocurrencies and traditional assets, with minimal fees and a strong reputation among users.