It's best to have both an introduction and a conclusion, but if you’re running short on time and can only have one, definitely pick the introduction.
In fact, your essay will be more coherent and more likely to score higher in Analysis if you focus your discussion on just a few points.
It's more important to show that you're able to pick out the most important parts of the argument and explain their function that it is to be able to identify every single persuasive device the author used.
If you're aiming for a top score, using advanced vocabulary appropriately is vital.
All the relevant information is in the passage, so avoid getting drawn into the topic and using your outside knowledge—you want to be sure to show that you’ve read the passage.