I've always used mysqli in the way I thought it was most convenient and never noticed any differences. Then came the question: why use object-oriented mysql? What are its advantages and disadvantages?
To make understanding easier, an example of what I'm saying:
$mysqli = mysqli_connect('127.0.0.1', 'usuario', 'senha', 'meusite');
$mysqli_query($mysqli, $comando);
And how would you look at objects:
$mysqli = new mysqli('127.0.0.1', 'usuario', 'senha', 'meusite');
$mysqli->query($comando);
Different this question, I would not want to just know what the best way. And yes to know in detail what differs between the 2 methods.