Split property into declaration and initialization
TypeScript requires to declare class properties. That means you have to always define property and type. To initialize property you can use the constructor.
Declare and initialize in the same line
When you know the initial value then TypeScript allows you to initialize a property in the same line. That means you do not have to even define the constructor. TypeScript will do it for you.
JS code after compilation
As you can see there is no difference between the two of them (you can see the preview on TS Playground) so you can choose what but personally I would choose the shortest (declare and initialize in the same line).