They have always approached football, business, and life in mostly disparate ways since Maclin was drafted a year after Jackson. Maclin is serious and workmanlike, but has a quiet confidence. He improved steadily in his first two seasons, but regressed in the last two for reasons both in and out of his control.
Jackson is flamboyant and cocky, but often introverted. He reached superstar heights in 2009 and '10, but went into decline in 2011, when he let his contract situation become a distraction. Last season he was better, but he missed five games because of injury.
They have yet to put it all together at the same time. Maclin recently said that Kelly's offense will balance the accounts after Jackson was the focal point in Andy Reid's offense.
But it's not as if Maclin hardly saw the ball. He actually has been targeted more per game than Jackson - 7.6 times to 7.2 - over the last three seasons. Wide-receivers coach Bob Bicknell said there will be plenty to go around in Kelly's up-tempo offense.
"We play right and left, and we're going a million miles an hour, so it's hard to say, 'Hey, he's getting the ball, he's getting the ball,' " Bicknell said. "They all better make plays."
Of great concern, naturally, is who will be distributing the ball. Both have previously made comments that suggest they would prefer Michael Vick.
Before practice was opened to the media in May, Maclin told reporters that Vick was ahead and that Nick Foles was only sprinkled in with the first team. In truth, the two quarterbacks split repetitions throughout the spring.
Earlier this month, Jackson said that he thought Vick would prevail. He backtracked Thursday, saying that "I just really took a guess," and that all the candidates "can contribute to helping us win."
Asked about the competition's possibly dragging on until the end of the preseason, Jackson said, "It's really good to know, but if we don't . . . then that's a part of our jobs."
Maclin was more diplomatic. "You can't get caught up in that, man," he said.
He has taken the same approach to his contract situation. Maclin, 25, is entering the last year of the five-year deal he signed as a rookie. Some may say he hasn't earned the right to hold out, but he said he never considered taking the stance Jackson and others have taken by skipping camp.
"How many of those guys got what they wanted?" Maclin said. "So that's how I look at it."
He said that he was "aware" of the contracts other receivers recently received. Mike Williams of the Buccaneers, who has similar career numbers, agreed Wednesday to a six-year, $40.25 million deal with $15 million guaranteed.
"I'm aware of everything that happens around me," Maclin said, "but I'm excited to go out there and prove what I'm worth."
Jackson missed 11 days of camp in 2011 and never received the extension he sought. He ended up signing for five years, $47 million with $15 million guaranteed, but his 2011 dip in production likely cost him millions.
The 26-year-old is entering the second year of his contract, but he isn't guaranteed any money after this season. He fired Drew Rosenhaus last month and now is represented by Vick's agent. Joel Segal is his third agent.
Maclin has been with the same agency his entire career.
Despite entertaining the idea of hiring rapper Jay Z's Roc Nation Sports agency, Jackson took a more traditional route. Still, he considers himself more of an entertainer than an athlete.
Jackson released a rap video, featuring Snoop Lion, this month.
"That's my other style," Jackson said. "That's something I like doing. I'm definitely a young kid, born and raised where I came from. So that's what's in me."
Asked whether he had a future after football that involved hip-hop, Jackson said: "Maybe, you never know. We'll just see how it works."
The same could be said about Jackson and Maclin's prospects in Kelly's offense and their futures in Philadelphia.
Contact Jeff McLane at firstname.lastname@example.org. Follow on Twitter @Jeff_McLane.