Headin out tomorrow to duck hunt for the first time. After googling it, I found that full choke is probably best but wanna see what OSA says. I believe we are going to be on the bank of FTG lake.
It depends on how you're set up and how the ducks are working. I usually use an IC choke for decoying ducks. I usually keep my chokes and wrench in a case in my blind bag in case I need to change it in the field. I don't remember having to do it though. Good luck tomorrow! I haven't had the chance to get out this year and we are super dry down here, but I hope to get out after new year's once or twice.
With modern shotguns and modern steel shot, I'd say modified at most. I typically go modified or IC. I really like #6 Hevi-shot. You get more pellets, so you can loosen up a choke for a bigger better pattern, yet they still have enough energy to penetrate down range.
Keep in mind steel shot usually patterns a little tighter than lead in the same choke. Therefore an improved cylinder with steel will likely pattern similar to lead in a modified choke. Decoying ducks on non pressured water hole an improved cylinder will be perfect.