If you were to purchase one of these organs which one would you choose and why?
SInce your sig says you have a Nord Piano 2, I'd probably go for the Hammond. The Nord may beat the SK for piano and samples as James says, but you already have all that in your NP2, so the only thing the E4D gives you is organ. I haven't heard the SK1 or E4D, but assuming that either would give you a satisfactory organ sound, as an NP2 owner, the E4D gives you nothing more, while the SK1 gives you a bunch of other sounds, the ability to split and layer its other sounds with the organ, and the ability to use it as a 3-zone MIDI controller where you can combine both internal and external sounds.
If you don't need any of that and really only care about organ sounds, it's just personal taste as to which you prefer the sound of and which keybed you prefer the feel of. Though also, if all you care about is organ functionality, I'd also look at the Numa Organ, which has only organ sounds, but probably sounds better than either of them, and may have the nicest organ action as well.