While Hulk's regenerative powers make them look weak in comparison. On multiple occasions, the Jade Giant has proven his healing factor is one of the best in the Marvel Universe, as he's been able to survive and quickly recover from some incredible dangerous attacks. But, unlike Deadpool, he can get better in an instant.
Hulk and Deadpool are among the many heroes in the Marvel Universe with healing factors - with Wolverine probably being the most notable character with the power. However, not all healing factors are born equal. For example, Deadpool can regenerate limbs, fill bullet holes, and heal damaged body parts, but it's not an instant process for the Merc with the Mouth - as it takes a little bit of time to recover from serious wounds and decapitations. Meanwhile, the Hulk has shown that his healing factor can work instantly, which makes the Marvel Comics hero that much more terrifying.
While there's been many instances of Hulk showing off his healing factor, a scene from Incredible Hulk #398 from Marvel Comics by Peter David, Dale Keown, Mark Farmer, Joe Rosen, and Glynis Oliver showed why the power is so much stronger than Deadpool's. In the comic, the villain Vector uses his powers to shred the skin off of the Hulk's body, as he's turned into flesh and bones. However, to Vector's surprise, the Hulk endures the blast and takes him out. As those surrounding the Jade Giant wonder if he needs help, Hulk tells them to shut up and regenerates his skin atop his mangled skin.
The Hulk's healing factor is one of the strongest there is, as his power to pretty much instantly recover from an injury has popped up on numerous occasions over the years. Even when chopped to pieces, the Hulk has eventually managed to make his body whole. Hopefully, by now, villains realize that killing the Hulk really isn't an option and is even more challenging than taking down Deadpool. Hulk can take a deadly blow and reform his body right away, which, combined with his strength, makes him a near-impossible out.
The Hulk is incredible for a reason, and a part of that is his amazing healing factor. While different writers and artists have changed the instantaneous nature of his healing factor over the years and tweaked it to fit the Marvel Comics stories he appeared, there's little question that the Hulk's healing factor is in the elite range when it comes to his fellow heroes. That's not to discredit Deadpool's healing factor, which is powerful in its own right, but it looks underpowered in comparison next to the Hulk's.
