Open or loose draw is with airflow all the way open.
It's really personal preference, For me, I find an open airy draw to have less flavor...I like a tighter draw...but that just my preference.
Honestly, with the GS Air tank that comes with the istick basic, there won't be that much difference. The airflow ring on that tank is a bit sloppy and the tank sits down in that well which kind of restricts the airflow anyway.