I guess this one is quite arguable, but if you're running out of manpower and have no money to pay mercenaries, I see no way to avoid Quantity.
If you wait until tech 4 or even longer, you could already have dozens and dozens of colonies. If you want to colonize, then you have to pick it now. Crucial in the first decades when the manpower is not so nice. Reduced coring cost and much much cheaper mercenaries.
I can just tell you what I would do myself, noting that I always seek for fast and risky expansion.
