Ok, maybe I will reconsider C++. But if you were building such app in C++ what third part solutions would you recommend for building multiplatform GUI? Qt? GT

Ok, maybe I will reconsider C++. But if you were building such app in C++ what third part solutions would you recommend for building multiplatform GUI? Qt? GTK? What is used now and what will be working/looking good on all three main platforms? (Mac/Linux/Windows)