Odell Beckham Jr. did.
This isn't to say Benjamin didn't play great for a rookie, he cracked 1,000 yards and scored 9 touchdowns, excellent totals, and was a huge addition for Newton and the Panthers, who entered the draft with a very suspect WR corp. Benjamin, if he continues developing, will be the big target receiver Carolina and Newton need to be successful in the passing game long term.
That being said, Beckham Jr. was better in about every metric, and what he did across 9 of the 12 games he played in was incredible. With 1199 yards and 9 TDs in 9 games, he surpassed Benjamin's full season production in half the games plus 1. He finished the season with 1,305 yards and 12 TDs.
Part of what makes Beckham so impressive is his catch %. He caught almost 69% of his targets. Benjamin, despite having 14 more targets, had 18 fewer catches, with a 50% catch rate.
The one attack on Beckham might be that his stats were so good across those 9 games that they must be an aberration. To an extent, that might be true (look at Patterson on the Vikings), but that doesn't detract from what he did during the season.
Now, looking forward, I imagine Beckham will come back down to Earth a bit, and Benajmin will continue to grow, but both will end up doing quite well. Which one is ultimately the better of the two depends on a variety of things, like injuries and systems, that we can't anticipate yet.