Whether you use hashes or arrays (or nested versions of them) really depends on how you want to access and use the data.

Hashes are referenced by a key, which is usually a word, whereas arrays are indexed by a number.

Imagine for a moment that your program keeps track of data for a car race. You could print out who was in the lead by referencing an array called $positions like this:-

print $position_driver[1];

Mansell

You could display what position a certain driver was in like this:-

print $driver_position{'Schumaker'};

2

Which you use depends which makes more sense to you.

You won't see much of a difference between them just from a declaration, you need to actually use them for that.