They are both fun, and free to play, so there’s no reason at all not to just try both and see which one you like better, or even to play both regularly.
War thunder is a work of art in today's pool of games. World of Tanks is played by more people and makes more money. Warthunder has better visuals, allows players to do more than just drive tanks. It's a better simulation of fighting with ww2 weapons systems than World of Tanks