I am trying to figure out where the action button should be located in an internal application where various tasks and data decisions are presented to a user. Each item has various content which could be very long or short depending on the nature of the item. I like the placement at the top because it would be a consistent placement for where decisions would be made and be easier to scan. However bottom placement may be more relevant since then the user can scan the items before making a decision.
I suggest put the button where users expect to see it. Also, consider the user’s path through the page.
In your design, for me is easier to press the button in the 4th case, but if the content is really long and the content is not essential in the moment I press the button for the action, 2nd option is better.
All these details (if is the main call-to-action button, if the content should be read before press it) are important for the decision.
Since you say that each item could be very long, I would go with your first option, and place them up top. This keeps it consistent no matter how long your content is. It also eliminates the need to have to scroll all the way to the bottom to perform an action which would be cumbersome on your longer length items.