I just like what Goodwin brings to the table more than Rondo. He's a better and more energetic defender at this point. Rondo is really lazy on defense at this stage in his career. He'll get steals here and there, he can help on boards, and in crucial 1-on-1 possessions (like against Fox) he can commit himself. But he's lazy over the course of a full game. He ball watches a lot especially off the ball.
And then on offense, Goodwin is much more of a threat to penetrate, which is a really important quality for your PG to have. He's not nearly as hesitant to shoot the three as Rondo is, and despite his career 3P% opposing defenses don't seem to grant him the three like they do Rondo, which in Rondo's case really hurts team spacing. I'm not convinced Rondo's 3P% so far is remotely sustainable either. Furthermore, Rondo is really turnover prone these days while Goodwin has done a great job taking care of the ball. Finally, Goodwin just plays faster which I like, whereas Rondo tends to dribble the air out of the ball at times.
Come playoffs, I can see Rondo being more useful than Goodwin. But I really like Goodwin as the backup PG for now over Rondo.