we use the following in the template declaration,

template <class T>

template<typename T>

 Is it that typename is preferred as it can be used for all types,
where as class can only be used for custom class types?

when the template parameter is not always a "class type"(including
/class/ /struct/, /union/), in this case, use /typename/:

e.g.

template <typename T>
class A { T t; };

class B {};

A<B>   a1;
A<int> a2; // int is not a class type

In the case when the template parameter should be a "class type", use
/class/,

Additionally, when the template argument is of template template
argument, only /class/ can be used.

e.g.

template <template <typename> class TT>
                               ^^^^^
class A;

HTH