For most users that would be fine, since I think many people simply have a preference one way or the other. However, it wouldn't address the annoyance for the users who mail direct and usually send now but occasionally use the queue to edit the recipients or add attachments.

I see big value in having the choice since the queue is quite useful, the users I've spoken about would like to be able to hit enter and zoom through rather than think about the choice (until they need the options the queue offers/want to save time and send now, depending on their preference).

Ken's suggestion is probably ideal over mine if offered on a per-user basis, since it makes more sense to have people expect it to simply always be set the way they like.