I'm gonna play the devil's advocate for the sake of argument and say WCW. Sure Hulk Hogan was WWE and made wrestling what it is today. He helped pushed the boundaries of wrestling when it started getting stale in his tenure in WCW and turned wrestling upside down on its head a second time as a much older man. While in WWE, Hogan has epic matches against Andre, Savage, Warrior, Taker, and Piper (three of the four he also faced again in WCW in lesser hyped matches) but also against guys who weren't all that big a deal like Slaughter, Earthquake, Sid Justice. Sure these guys were big at the time, but nowhere near as big on average as the competition Hogan faced in WCW. Hogan wrestled perhaps once every three months while champ in his first major WWE run as champ from 1984 to 1990. In WCW, he defended the title about twice a month and against much stronger competition in Goldberg, Sting, Luger, Flair, Big Show, DDP, Nash, Hall, etc. Mind you most of his matches ended in DQ with an NWO run in. But there was so much talent there and so much more competition that guys like Guerrero, Benoit, Jericho, etc never had the opportunity to climb up the ranks to get to Hogan while he was champ. Hogan was world champ for an entire year, fending off about 30 of the best 40 wrestlers in either promotion.
Hogan was also the leader of the greatest stable in wrestling history, the New World Order, and his Hollywood persona made him hands down the most entertaining and hated heel in history. Nobody before or after could get garbage thrown at him like that, nobody before or after could get senior citizens in the crowd to stick up their middle fingers and stop coming to the shows, nobody before him or after could create so much heat that it would destroy his chances in the future of ever being able to achieve any long term success as a babyface. Hulk Hogan was the biggest face in WWE history but he was by far a better heel in wrestling history period in the WCW as leader of the NWO. If Hogan were to go back to his heel character now, Hogan could very well change wrestling for a third time, even as a 60 year old overexposed cripple.
I know this isn't how a lot of recent wrestling fans and WWE marks see it, but I watched Hogan from 1984 till 2003 and his performances on WCW Nitro, Thunder and at pay per views were just as epic to me as his Survivor Series' and Summerslams. When I want to watch old wrestling, I just youtube WCW Nitro. I could care less about his so called epic matches with Tugboat. However, nothing WCW did could match Wrestlemania and therefore Hogan's epic WM performances (like against Andre, Savage, Warrior, Rock) beat out WCW by far in it's grand stage epicness (vs Sting, Savage, Goldberg). But on a day-to-day, month-to-month basis on live TV and at pay per views for a 3 year period (the WWE equivalent of Hogan's first 9 year run) I found his WCW time just as memorable as his WWE run.
I feel the only good reason fans here think its WWE hands down is that in 1984-1993 WWE was watched and loved by everyone and Hulk Hogan was the WWE..during his WCW run he was WCW but there was also 30 big names alongside him helping carry the company. Some were young guys who were amazing wrestlers (Benoit, Jericho, Guerrero) and some were very well established and almost as big (Flair, Savage, Sting). Hogan didn't have to be the entire focus of WCW because wrestling had changed. Not everyone loved WCW, a lot of people refused to watch and still hate it to this day. In fact, some people look back and see WCW as a blip on the wrestling radar. Since only about half of the wrestling audience Hogan had his first WWE run wasn't watching his big WCW run, one could argue Hogan had a better run where he was loved and watched by an undivided audience rather than where he was watched and appreciated by WCW fans while usually watched and despised by WWE fans.