I'm one of those people for whom the security aspect is far more important (*) than data loss -- data loss can happen for so many other reasons that one should have a good, reliable, backup regime anyway, so one more reason doesn't bother me.
So ext3: people with my mindset should stick with data=ordered. (I don't see guarded as being too useful for ext3 -- we'll probably have switched to ext4 by the time guarded becomes mainstream).
Ext4: I think I'll stick with ordered here too. If the overhead has been much reduced by delayed alloc, it correspondingly reduces the main advantage of writeback too :-) I'd rather err on the side of security when the difference is minor.
Although collectively we like choice, and we *need* choice, when it comes to actual usage, we have to rationally reduce the many choices available into one and say "*this* is what we will use"!
Thanks once again for jumping in and helping with that!
(*) My home desktop is used by my kids also, for instance -- so it *is* a multi-user machine in the old traditional sense. The work machine runs email and office apps as one user, and my web browser and IRC as another user (simultaneously), so -- while both users are still me -- it too is multi user in the sense of wanting to keep two disparate sets of files separate.