has a negative connotation. There is some suggestion that if you are in a rut, that you are aren't thinking about what you are doing. You are acting as though you were in a trap.
, on the other hand, need not be a bad thing. It can be a pleasant set of habits, or something that helps you get more done. Ted defends himself by saying that he is not in a rut (He isn't trapped by his habits); he has a routine (He has a habitual way of doing things and he enjoys it).
: conotação negativa.Routine
: rotina, sem necessariamente ser ruim.
E.g.: It's not a rut, okay? It's a routine and I like it.Ref. Wordreference