if you plan to have another bag on you, i'd suggest the swingpack because it's flat on the body and it holds just the essentials, money, keys, etc.
the duffle can be worn two ways, so that's why you might want to lean towards it, plus it can hold a diaper better! but if you have another bag for that it isn't necessary.
plus the swingpack is good for when you travel later on, e.g. to put passport.
i'm more inclined to the swingpack just because it's like a bigger version of the wristlet - intended for just going out and leaves your hands free
the duffle can be worn two ways, so that's why you might want to lean towards it, plus it can hold a diaper better! but if you have another bag for that it isn't necessary.
plus the swingpack is good for when you travel later on, e.g. to put passport.
i'm more inclined to the swingpack just because it's like a bigger version of the wristlet - intended for just going out and leaves your hands free