I think it's hard to say for sure. Different people might have different opinions on who the main character is depending on their interpretation of the story.
The main character in 'Mr President' manhwa is typically a complex and dynamic individual whose actions drive the story forward. But without specific details, it's hard to pinpoint exactly who it is.
The Omniscient Reader manhwa is quite faithful. It does a good job of presenting the plot and characters as they were in the original. Some minor details might be tweaked for better visual or narrative flow, but the core remains intact.
It depends on personal preference. If you like visual media and want to see the story come to life with cool art and action scenes, then the manhwa might be better for you. But if you enjoy using your imagination and delving deep into the characters' thoughts and the more detailed world - building, the novel could be the better choice.