Assuming that you won't have Town Portal or Lloyd's Beacon when you want to tavel at first between Harmondale, Bracada & Barrow Downs, you also have to take account of travel times. You can get to Bracada from Harmondale in 5 days if you leave Harmondale for Erathia on a Monday and take Wednesday's stage from Erathia to Bracada - there are no stages going directly from Harmondale to Bracada. If you walk, you have to go via either Erathia or the Barrow Downs, and if you're going to do that, you might as well visit the Barrow Downs first anyway. Other advantages of doing this are that Barrow Downs IMO is significantly easier than Bracada if you have to do any fighting, and you can collect the items you need for the first sorcerer promo from Barrow Downs before getting the quest from Thomas Grey. Additionally, there's a quite nice chest in the Barrow Downs 
. All things considered, I would tend to do Barrow Downs first.
But hey, one of the strengths of the MM games is the amount of non-linearity in them. You do whatever suits you best.
