1) Does a default program or an email send program trigger faster in the Campaign Queue?
2) Does a batch or a trigger smart campaign trigger faster in terms of order of operations?
3) Does a wait step deprioritize a campaign in the campaign queue?
I'm pretty sure I don't have all the answers, but me let me try as good as I can.
First of all, this priority list is still valid as far as I know:
1) I don't think it makes a difference
2) That depends on your setup. As far as I know, batches and triggers work independently from each other, and if your batches are queued and your triggers are not, trigger campaign will work quicker. And the other way round. We for instance had long queues in our trigger processing a while ago, then we moved a lot of processes to batches, and now we have backlogs in batch processing...
3. Yes, see table above. Yet only if the wait step comes first.
One big advantage of the email program (mailbox) is that you can use Head Start. Marketo will start compiling your emails and getting everything ready 12 hours ahead of time, so that when the time for the send comes, everything goes out much faster.