#1 Bobby Lashley
If WWE does decide to hold off on doing Roman Reigns vs. Braun Strowman next, then I can definitely see them doing another Reigns vs. Bobby Lashley match for the title at next month's Hell in a Cell show.
Lashley was the only top Raw star who didn't have a match on the SummerSlam card, so perhaps he'll have to earn an opportunity at the Universal Championship on Monday's Raw show, or WWE could go with the idea that they're 1-1 against each other, and that they'll have the rubber match at Hell in a Cell.
Aside from Lashley, there really isn't anyone else on the Raw roster who is credible enough to challenge for the brand's top title. In fact, all three potential opponents on this list are babyfaces, which pretty much tells you that the red brand is badly lacking main-event level heels.
But, perhaps they'll change that during Raw by turning one of the three aforementioned names, or, and this is highly unlikely, they'll finally turn Reigns
No matter what WWE ends up doing, the fans are likely in agreement that it's good to finally have a full-time World Champion on Raw again.