The most likely choices for Zoom are Eddie Thawne, Henry Allen, Barry from Earth-2, and yet I believe none of these is that bastard speedster. Also one could ponder that he could be Eobard Thawne from Earth-2.
I believe that Zoom has been under our noises this whole time in Jay Garrick. I completely understand why the writers of Flash are introducing Wally West and Jesse Quick to fight Zoom.( Hold on I will get why I think Jay is Zoom) I believe this is a smoke screen for the battle of the force. The key person ( he really needs to step his game up) to help slow Zoom down is Cisco " Vibe" Ramon. In the New 52 ( I will not dive into his powers ) Vibe can disrupt the speedforce , giving Barry and the rest a chance. Vibe is very powerful and I have been wondering why did Zoom leave so fast after Cisco shot him with the dart. Maybe Zoom was scared if they touch Cisco would know.
Many reasons why I think Jay is Zoom. First off when Barry fought Zoom he did not lose his powers ( no I don't think Jay is suffering from PTSD and where in the fight did he lose his powers, made-up story .) Secondly when Jay's helmet came through the wormhole in the season finale Thawne was scared. Also I believed during Earth-2 flashbacks Jay was using a Velocity drug to imitate a speedster( he is a scientist). You can ask why did he save Harry. Zoom might want him to see his daughter's death? I do not yet understand the infacuation with Harry? Also Jay has been the Flash just a little longer than Barry, yet better verse in the force. I could go on, but no one would want to read it. Also the test Snow ran I am not sure entirely how the speedforce works. Lastly they're ( Zoom and Jay) same size and also has the same exact EYES. I could be so off, but maybe not. Leave a comment on how crazy or right I am! I truly love to guess things like this!