What sort of paddle should I choose? It depends on the purpose of the paddle. The more you use it, sooner you will buy a better paddle...
Sup paddles may already come with the boards. These are mostly aluminium. But some brands are already adding some better paddles.
Aluminium paddles are heavy. They are suitable for beginners and for those who just want to have fun on holiday. I should point out that aluminium is a metal and it does not float. Most paddles have a clogged tube and trapped air keeps the paddle afloat. However, do not leave such a paddle on the water. It will sink sooner or later. Some aluminium paddles have an extra paddle blade and can be turned into kayak paddle so you can have fun sitting on the SUP.
Better paddles are made of fiberglass or carbon. The best paddles are full carbon. Such paddles are less than half the weight of aluminium paddles.