Chopping. Vision Impulse, B2k3w/pds, evil omen = 3 markers that won't chop, so no real advantage.
Consistency/accuracy, they're all pretty close no marker jumps out at me as being significantly more consistent than the others.
Kick is a category that I think of when measuring guns, although it is related to consistency... anyways... omen will have more kick than the other 2, hands down... while the other two are similar enough to not merit a big nod in either's direction.
Speed. A stock omen will go up to 15, although most people can only get it to around 13. That might be fast enough for you, or you might need more pop which the other markers can provide. Or you can slap a morlock on the omen and leave the other markers in the dust
Maintenance. This tips towards the omen... Notwithstanding the production issues with some of the earlier models, the omens are solid guns that require minimum service to maintain peak performance. All you really need to do is lube the hammer.
Reliability. I've never owned an impy so I can't measure it with an omen. I've had a bushy though and it was very solid. My omen though has been just as solid. The one exception to omen reliability is that the bumper will need changing on occassion.
Price. Omen all the way. Unless you go for a non-vision impy, which is just not cool anymore
Most importantly: your opinion. The most important component in balancing what you like the best, is to try all three and make your decision that way. Everyone's different, there is no one gun that is better than every other.