Stay - More opportunities on SmackDown Live

It's arguable, but Dean Ambrose moving to Raw might have been great for the Shield and WWE, but it was the worst possible thing for his singles' career.
When he was on SmackDown Live as technically it's first champion, he was the top dog on the show. He carried the show during the initial stages of the brand split and helped make AJ Styles the star he is today.
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Once he was a member of Raw, his stock took a drastic hit. Sure, he was a member of the popular faction once again, but in the hierarchy of the Shield, he's at the bottom of the trio.
A lot of what Drew McIntyre and Dolph Ziggler said during their feud with the Shield was true. Reigns was always the 'top dog' and Rollins was when Reigns wasn't.
Ambrose was always considered for challenging in the main event on Raw but never considered for carrying the show like he did on SmackDown.
If he was shifted back to the blue brand, a lot would open up for him. He could still be a heel, but the dynamic on that show has changed.
Daniel Bryan is back and now a heel champion and Superstars like Andrade, Mustafa Ali, Rey Mysterio, Jeff Hardy and Samoa Joe all would be perfect for Ambrose to feud with.
And then there is Shinsuke Nakamura, Rusev and any number of call-ups from NXT that might land on SmackDown.
When all is said and done, a shift back to SmackDown might have made things more tolerable for Dean Ambrose rather than rehashing the Shield heydays and being the third-most important member of a trio of superstars.