Which is the better scheme for a poster: “tell a story” or “important first”?
This may be field dependent, but anyway, I'll tell you my (hopefully educated) opinion.

The conclusion should be at the end. It's sometimes criticized that some research starts with a conclusion and then start doing some p-fishing and other unethical practices to support that conclusion. You may present the question that you are trying to answer and as a "spoiler" the answer to that question, as it is not infrequent in the abstract, but that doesn't eliminate the need to present the conclusion in the end, explaining how do you get to that conclusion from everything else, in a very (straight)forward way.

In short, wrt to your question, you may (or may not) introduce the results at the beginning, but the conclusion should be at the end in any case, explaining how do you get to it.

Additionally to your question, it's nice (not required, but definitively good) to explain why the objective set in the first place is important. This may not be needed in some cases, e.g. curing cancer, obviously everybody thinks finding a cure for cancer is important. However, if your objective is deciding whether plastic bottles should be taller or wider then maybe you should explain the impact that a shape change could imply in terms of sustainability, before explaining what are you trying to do (e.g. reduce the amount of plastic needed).