i have six array elements, what usage is better than others, and why? : <p>i have six variables, what usage is better than others, and why?</p>

<pre><code>$a["1"];
$a1['1'];
$a2[1];
$b['b'];
$b1["b"];
$b2[b];
</code></pre>

<p>question is only about code optimization, can't really understand what of that is better than other</p>
