I have both. I think the crown is a litle easier to shoot from a bench, accurately. The impact is nice if you like sit in the car, and shoot out the window. It is also easier to carry, as I can carry it in one arm, while the barrel is hanging down (maybe not with the longest barrels) If you like to tune and experiment allot, the impact have all the adjustments accessible externally. The crown also have good adjustments, within the limits of the power wheel. The only thing I did not like on the crown is that If I have to change the hammer spring tensioner on the powerwheel, the stock has to be taken off. It is a litle cumbersome as the powerwheel, which has some small balls, can easy fall out, and dissapear if not carefull. It bothered me so much, that I actually modified my stock, to get acces to that litle hex screw on the power wheel. If you plan to shoot heavy slugs in high power, the impact have more options. The impact have many 0-rings, and parts, and might need service sooner than the crown, some time in the future. I personally have not owned either of my guns that long, so both have been without failures.
Both are nice guns, but the decision is your own. If you mainly want to hunt, the impact is easier to carry around in the field (I am not a hunter myself). It also depends on the budget, as the impact is more expensive. The best option for you would probably be if you could go to a range and try both, and see which one you like the most. The choice can be as simple as if you like a bullpup better than a classic rifle.
BTW matt dubber has a nice comparison video on both guns: https://www.youtube.com/watch?v=gYaUN4qJ5D4