Which is best - $vbulletin->db->query_read OR $db->query_read

[Mr Happy]

Just a very quick question.

I'm wondering what's the difference between

$vbulletin->db->query_read(Select bla bla bla .....

and

$db->query_read(Select bla bla bla .....

Trying to write my first mod for vBulletin 4.x (wish me luck I'll need it :P ) and wondering which is the best to use.

I've being using lots of the tutorials and other posts as references but I'm not sure which is best practice. Both seam to work fine.