they don't have so much difference,,a little difference in emotional feeling
向来means he always behave like that,,,kind of habit.
总是gives the person who speaks it a sense of disagree or repel, like I say: "Xiaoming always watch TV( so I don't like it,maybe it will cause his school scores going down) , Or I say :"He always eat my pancake( so I can not eat it,so I hate it)"