Array vs If, which one is better in performance/best practice sight?

For same result I can use (I prefer this simple one, personally):

$idx = 2;
$arr = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
echo $arr[$idx];

or:

$idx = 2;
if ($idx == 0)
    echo "Sun";
elseif ($idx == 1)
    echo "Mon";
elseif ($idx == 2)
    echo "Tue";
elseif ($idx == 3)
    echo "Wed";
elseif ($idx == 4)
    echo "Thu";
elseif ($idx == 5)
    echo "Fri";
else
    echo "Sat";

Which one is better in performance or best practice perspective?