I quite like the idea of it being Soran.
Personally, I found John Harrison, a man of mysterious origins, superior intellect, who had access to some pretty advanced technology to be a far more interesting prospect as a villain for the film, rather than Khan. It could have allowed for some far more interesting story-telling as to what Harrison's motives were (for a man from a race who've left behind all the pettiness and greed of our generation) and what his ultimate goal was.
You know, something original.
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)