If they both have the bag,then you could either choose the one closest to you,and if they're similar distances,choose the boutique. That way you're dealing more directly if (heaven forbid) there should be any problems down the line.
If you're not sure you're going to keep the bag,maybe use the department store since you only get store credit at boutiques and only within 8 days.
I hate when people take bags home and return them though. I'm sure sooooo many people in the US are buying used bags "new".