I believe DJ with have the greatest immediate impact among all the rookies this year for the following reasons.
1. He will play more than Ellington, not because he is better, but because he is more durable.
2. He is a big, versatile back who can make people miss. But he also has the strength to move a pile. I am not sure why you did not see that on his videos. He does it, just not alot. Of course, if you can make a defender miss, its usually the better option over trying to run through him.
3. He has exceptional hands out of the backfield, which makes him tremendously versatile. He is also a good route runner.
4. the Offensive line will be improved.
5. RB is the easiest position to make an immediate impact.
Its funny how players are often all-or-nothing with fans. Beanie was a very good back. He just could not stay healthy. Toward the end he started playing to not get hurt, and that caused him to diminish quickly.