Use both. When I go with a friend of mine I use a 12 gauge to shoot the flyers and he uses a .17 HMR to shoot the perchers. Ive hunted them in fields with layout blinds and decoys that works well but before I had that stuff I would find an open spot in the canopy of a woods (when the leaves are on) and set up calling there. Most of the time they would just fly over to check it out and by the time they saw you it was too late. Not a good tactic if you have a sore neck though, youll be resting your head on your shoulder blades almost the whole time. A scattergun is imperative in this situation. I normally use a heavy 3" 5 shot (about $10/box) or you can get away with using 2 3/4" 6 shot heavy game load (about $6/box). There was a question on here about why they are more comfortable over water. My theory would be that they dont have any preditors on the water. Its not like a great white shark is going to leap from the deapths and pick em out of the sky or even a 50" musky for that matter. I think crows are greatly underestimated they are actually very smart. Their very communicative having different tones for danger, distress, food, etc. One wrong "squawk" could send them into the next county. Given that...Good calling could bring em from the next county. Crow vocabulary is much greater than with ducks and geese. Sure we all use tons of different sounds when calling ducks but real live ducks basically only have 3 different sounds; hail, quack or grunt, and chuckle. As hunters we throw in the comeback call the greeting call the laydown call, etc. With crows its almost like morse code. Ive heard 1 long with 3 shorts, 5 shorts, 3 longs etc. Im not sure what it means and I really dont think anyone, even scientists can understand a crows language completely. When Ive heard crows in real life it seems like the 1 long and 3 shorts is a no no every time I hear that the crows are hightailing it out of here, but 5 shorts followed by 3 longs will usually bring in other crows, dont ask me what it means, those are just observations made sitting on my front porch watching them fly around, out of season. Are these observations false? No. Are they coincidence? Maybe. Do I really know what Im talking about? No. Do I type fast and have a tendency to ramble on about useless facts and otherwise wasted knowledge? Yes.
treat every situation like a dog. If you cant eat it or hump it just piss on it and walk away