Which is a better way to check if an array has more than one element?

Use this

if (sizeof($arr) > 1) {
     ....
}

Or

if (count($arr) > 1) {
     ....
}

sizeof() is an alias for count(), they work the same.

Edit: Answering the second part of the question: The two lines of codes in the question are not alternative methods, they perform different functions. The first checks if the value at $arr['1'] is set, while the second returns the number of elements in the array.

if (count($arr) >= 2)
{
  // array has at least 2 elements
}

sizeof() is an alias for count(). Both work with non-arrays too, but they will only return values greater than 1 if the argument is either an array or a Countable object, so you're pretty safe with this.

if(is_array($arr) && count($arr) > 1)

Just to be sure that $arr is indeed an array.

sizeof is an alias of count, I prefer to use count because:

1. 1 less character to type
2. sizeof at a quick glance might mean a size of an array in terms of memory, too technical :(