#1 Drew McIntyre

Unlike how Shinsuke Nakamura won the 2018 Royal Rumble and failed to win the WWE Championship, Drew McIntyre will be booked to make his victory worthwhile. Paul Heyman is behind the Scottish Psychopath which is why he was picked to not only eliminate Lesnar but also win the whole match.
McIntyre has long been more than ready to run with the ball on RAW, but for whatever reason, he was never given the chance as a major Champ since returning in 2018. That started to change when he began to mention on RAW that he'd never received a major title shot. It would have been nothing had he mentioned it once but he consistently said it each week until the Rumble.
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Brock Lesnar exists in the WWE hierarchy as an unstoppable monster or the ultimate obstacle. Once a Superstar topples The Beast, they are a made man. Rollins and Reigns were already made men when they defeated Lesnar but they were still propelled further into the history books by taking titles from The Beast.
If WWE wants to treat McIntyre like the Superstar that we've all been seeing since his return, then he's winning the WWE Championship at WrestleMania. He's more than deserving of the title and Lesnar usually takes time off from the company after 'Mania. It's McIntyre's chance this year and he'll make good on the opportunity by winning his first major title.