#define action1 1
#define action2 2
#define action3 3

main()
{
    ENTITY* aPointer;
    //specifying a pointer allows you to send it/manipulate it later in this or other functions
    aPointer = spawnFunction(action1);
}

//Usually I'd specify 2 or 3 variables for the vector in 
//order to place it where you want but it's really up to you.
ENTITY* spawnFunction(int action)
{
    if(action == action1)
    {
       ent_create("default.mdl", vector(0, 50, 100), yourAction1);
    }
    else if (action == action2)
    {
       ent_create("raptor.mdl", vector(0, 50, 100), yourAction2);
    }
    else if (action == action3)
    {
       ent_create("tower.mdl", vector(0, 50, 100), yourAction3);
    }
    else
    {
        //you could write an error, or whatever here, it's good practice to use error checking
    }
    return my;
}

//Usually defined somewhere else, like another file
action yourAction1()
{
...
}
action yourAction2()
{
...
}
action yourAction3()
{
...
}