Not a big fan of any of them.
In a cinematic universe where casting has been exceptional both are ...average at best. Maybe that's the problem: maybe RDJ is SO Tony Stark ( to the point that the character in comics has become RDJ) and Hemsworth is so Thor,etc. that makes Ruffalo/Norton just "meh!"( even to this day: Pugh, Harbour and Weisz are A+). They both a lack an essential tragic element that yeah, try, but not achieve.Among all the characters created by Lee/Kirby this is the one that best represent the Frankenstein Syndrome ( our fear about how the technology can change us) and is difficult to see this is the MCU.
The character itself does not help either. The fundamental concept of Hulk is understanding this is no schizophrenia, this is not a malfunction of Banner psique. The Gamma accident created a different persona that now has to share a physical identity (not body) with Banner.
This is the premise writters have used for the last 20 years because they understood it is the only Hulk that works and the MCU did not fully adapt to this because we have "Hulk Smash!!" in Avengers transitioning into a separate persona in "Ragnarok" tansitioning into "Banner is in charge" in End Game.
The stupid Hulk is another aspect that got erased for the last 2 decades because it just did not work. Hulk was born in the accident so for the first years you can see him in a child state: learning and understanding his enviroment that is usually very hostile ( thank you Gen. Ross!!). Over the course of the years the character evolved and got into a mature state where the "Leave Hulk Alone!!" is no more a thing. The stupid Hulk just does not work anymore, everybody understood this ( but the MCU) because although he is not about solving diferential equations (that's for Maestro and Proff. Hulk) he shows a high tactical intelligence ( many...many...storyarcs where he wins by using the right tactic not just Smash!!). The best comparision would be Conan: is Conan stupid? No, not really. He probably knows shit about maths but he is extremely smart about his craft: fighting.
Does anyone not love Planet Hulk/World War Hulk? Anyone? Because I have yet to meet a single person who don't. This is the right Hulk.
So it's a combination of factors that gets piled on top of each other:
1. Not setting a clear distinction about Banner/Hulk persona.
2. Getting back to the primitive stupid Hulk we haven't seen for decades.
3. Some weird course correction in the story like the Natasha affair that got solved in a head nod "Hey!", "hey!" in Infinite War ( that was...fucking weird)
4. A narrative that usually uses him as a mechanism for other characters shine ( the fight in the Helicarrier vs Thor, the fight against the Hulkbuster...)
...and the most incomprehensible of all ( i'm still scratching my head in confussion): not-a-single moment of "Ohhh Fuck,fuck,fuck....Hulk is REALLY angry now...big mistake. Now hulk is gonna smash". The closest ( and is nowhere near that) is the Hulkbuster breaking a tooth and I don't say the "That's my secret Captain. I'm always angry" moment is not cool ,no, it's really cool but does not capture the idea of a emotional breakdown that triggers the Hulk real strength. Instead of using Nat's death to do that...he throws a bank to a lake...../Iwantocryjpg. There's narrative tools in the comics that just can't be translated into a film...and this is not one of them: a Hulk outburst could be a fantastic cinematographic moment and they just choose to not use it.
So what can I say? I don't know if Marvel Studios always saw him as a secondary character ( in almost 6 hours of Inifity Saga he is in....the first 5 minutes) and I don't know the extent of how the licensing affected but we have a not great casting ( not awful either) dumped into a character that most of the times looks accesory to the story.
It was fucking difficult for Norton/Ruffalo to shine in this context.