1) Barry Allen
If this article has made anything clear to you, it should be that time travel and alternate realities are a very confusing thing. Barry Allen being Savitar would be seriously weird, but it could work, especially if he hails from a different world or timeline.
What if Savitar is the Barry from the Flashpoint timeline? Our Barry has memories of that, but some sort of echo being left behind in the Speed Force could lead to his arrival in the present in some form, not to mention it would go a long way in making Flashpoint feel vastly more important after it lasted for all of a single episode.
Savitar has said that he was the first Speedster, and that’s something we all know Barry was on Earth-1, so this being a twisted version of him could explain his eventual transformation into the character. It will take The Flash‘s writers a lot to make this work, but if they can figure it out, this is one reveal which could really prove to be a mind-blowing and memorable twist.