CM Punk was great with The Rock, Undertaker, and Brock Lesnar. He's always hit it out the park with John Cena. The catch is The Undertaker, Rock, Brock, and Cena were and have been great before Punk.
Punk has just had stinkers with Ambrose, Rollins, and Reigns especially when you compare him working vs them to the Rhodes Brothers, Kane, Rey, Usos, Bryan, and Cena. They click with the Shield he doesn't. It is not just the Shield either as he and Ryback stunk up the joint for months on end.
He's simply hit or miss with the right guy. It can be motivation, it can be injury, or it can just be he's not a Shawn Michaels in a ring and can't click with almost anyone.
A break could do him well with the way his matches have been going lately. In fact I'm kinda hoping he doesn't get Trips at all at Mania and its Cena or Bryan in there to help pull the best out of him because as it is right now, Trips would have to be the one stepping it up to another level to carry Punk along out his funk.