hmmmm....before i answer i have to disagree....
yes there are good rivalies out there that have helped and/or made a wrestlers career more memorable but a lot of big time wrestlers never had a long time fued and are big stars....
HHH, HBK, Undertaker, Hogan.....huge names who never had a long time fued...lots of fueds yes but not multiple big matches over the course of years
And I would have to tell you that your completely wrong.
HHH, How long did he feud with Owen Hart? Then he had a two year brutal rivalry with HBK.
HBK, look at above for one. Then let me remind you of a name. How does Bret Hart sound? These two feuded forever back in the day. Not only in ring, but out of the ring.
Hogan, Is the one that you may be the closes with but still. Back in the 80s he had a nice long feud with Savage. As well as Warrior..(I actually don't remember how long that was... So it might not fit.)
Undertaker, How bout his feud with Mankind? Or his feud with HBK. Now I'll admit that his feud with HBK wasn't as long, but it was still longer than most now days.
Back on point. I agree with Morrison, being Punk's rival. Who else is there really for it to be? Someone on earlier said the Undertaker. I just can't see it happening, because Taker is in last little bit of his career. I would love to see these to in the ring, but as for Punks rival. Not going to happen.
Jericho is the only one that I can see going with Punk, but like Disarray said, they are both better has heel's. Now I don't know about Morrison, because I don't think that he's hit his full potential as a face. So right now I think that Morrison has the chance to be the Rival.