I've been watching some videos and it seems the resonators need to come off for any kind of sound difference.
Looking to get magnaflow 18" and wondering if the resonators should come off to make any difference
I would say no. I have a Flowmaster Outlaw and it sounds awesome. It was a simple muffler switch, and trust me, my truck is loud (in a good way).
There are many examples of people on this forum switching mufflers but having to go back due to the sound being so much louder than they expected. So no, you don't have to remove the resonators to have a change in sound.
The resonators in the rear have 4 weep holes each (2 front & 2 rear), so they sound rather "airy" at cold start, but you can cover the rear weep holes with JB weld and leave the ones in the front open for moisture removal. The front resonator helps with reducing cab drone at highway speeds, I would leave that one alone.
Unless you go with a tuned aftermarket exhaust (like Borla) however, you will get a resonance/drone when the truck is in MDS 4-cylinder mode. I simply disable my MDS, which I would do anyways regardless.