First of all, congrats on baby #3!!!
I would go w/ the Bloomsbury.
The speedy b 30 is a great bag (and I love mine) but it's not small. It holds a considerable amount and I don't find I carry all that much most days. So, unless I'm carry more than usual (extra tablets, schoolwork for kids, etc), I don't reach for it. If you consider at some point you will be carrying a diaper bag also, that just gets to be a bit much (especially when you factor in the infant carrier or keeping tabs on older kids, too).
What I like about the Bloomsbury is it's slim and feels more like a true cross body to me. Perfect for running errands w/ the kids in tow. Material is very forgiving and will withstand all kinds of infant/child accidents (cleans easily).
I am a HUGE fan of going into the store and trying things on. I remember trying on a bag and then holding my 3yr old's hand and walking around the store to see how well the bag stayed on my shoulder, etc.
I don't think any of them are wrong and your needs and tastes may evolve but each of these choices will fit your needs off and on for years to come.