What s quicker and better to determine if an array key exists in PHP

Question

$key = 'jim';

// example 1
if (isset($array[$key])) {
    // ...
}

// example 2    
if (array_key_exists($key, $array)) {
    // ...
}

Out of these two examples which one is a better option? I usually use the first one but I have seen people using the second one more. So can someone please tell me which one is a better option?