Arrays are faster for almost everything, by an order of magnitude. Particularly in Objective-C, which is how they'd be implemented.

The process of looking up, via a key, is quite slow, when compared with index lookups of arrays.

When it comes to iterating through one or the other, arrays are often much more than an order of magnitude faster due to their inherently streamlined memory usage.

Then there's unpacking.

When you store x, y and rotation in a dictionary at a key, you have to "unpack" that to use it, which takes even longer.

So you're best off having an array for each:

arrayX
arrayY
arrayRotation
arrayObjectName

and iterating through when you need.