Punk's reign was good but he main evented like 3 PPVs. WWE always put John Cena ahead. Even when he was having shit matches with the likes of Kane, Big Show and Johnny fucking Ace. This was all happening while Punk was putting on 4-5 star matches with the likes of Bryan, Jericho and Del Rio.
Unbelievable stuff from WWE. And don't give me this "entertainment" BS. There was nothing entertaining about those shit Cena matches and feuds.
Nothing ruins a title reign like beating the same guy over and over again. Sheamus had about four title matches with Del Rio and it got incredibly boring.
Short reigns can be good but there must be a legendary match somewhere along the line. The Rock once held the WWE title for only 35 days but had the match against Austin at Wrestlemania X-7. Mick Foley held it for 26 days but the win on Raw was extremely memorable and the I Quit match he lost it in is the same.
Winning the title from a top star like Cena and then holding it for a good three to four odd months while being booked in decent feuds with decent wrestlers makes a real good title reign in my opinion.