WHOA, i think the baggy gm would look AWESOME as a messenger...why didnt i think of that!?
i personally find a lot of the damier messengers and monogram messengers really dull most times...i think making one of the other lines work for you in a new way (ie baggy gm as a messenger) is the best way to go...but thats just me.
some of my favorite messengers are a) discontinued and therefore on ebay for, sometimes, a lot of dough, or b) are shapes not normally associated with messengers (my taiga beloukha...case in point).
go for something different, skip the predictable naviglio or abbesses. again, thats just me...