#4 Samoa Joe vs AJ Styles
If WWE didn't care about using one of the best NJPW rivalries in recent memory on television and at WrestleMania, using the two cornerstones of TNA won't be a problem either. AJ Styles and Samoa Joe are money together and pitting them against each other would hands down be one of the best things WWE can do at the moment.
Joe is red-hot property right now. He is just back from an injury layoff and is eviscerating the character of Roman Reigns on a daily basis. Even if Joe is made to lose their blowoff match at Backlash, Joe can be rebuilt into being the next big contender for AJ Styles. Even if it isn't for the title, Joe and Styles is a match that would have fans salivating.
Honestly, WWE should throw caution to the wind and just have these two men do whatever they want. Don't give them simple 1 on 1 matches, add stipulations. Imagine Styles and Joe in an Iron Man match; Imagine a brutal No Disqualification match. There are so many possibilities with this rivalry.
Joe is an absolute brute, and Styles is the fighting underdog. They are the perfect face-heel pairing and WWE need to push this rivalry forward. Have Joe demolish Styles and ultimately give him the upper hand over Joe after he is tired of being outsmarted.
The never-say-die babyface is a lost art (after John Cena overdid that shtick) but Styles can bring it back perfectly.