Mainly We Used Kodular
There are several platforms of app inventor like Thunkable , Appybuilder, Makeroid and Droid Maker. In Between I would like to prefer Makeroid because of its advanced components and design.
The Second Best Platfrom is Appybuilder
Appybuilder is most stable app inventor platform. In appybuilder their is also lots of component present buy makeroid has more components than appybuilder.