A single stroller that grows into a double — add a RumbleSeat or a second bassinet and it carries two without buying a whole new frame.
If you're staring down a second baby (or planning one), the Vista is the smartest long game in this category. You start with one seat and later add a RumbleSeat, a second toddler seat, a bassinet, or a PiggyBack board for up to three kids on one frame — no new stroller required. It steers beautifully for something this substantial, the huge basket actually swallows a diaper bag plus groceries, and UppaBaby's build quality and customer service are genuinely excellent. Honest caveats: fully loaded with two seats it's heavy and the fold is bulky in a small trunk, the RumbleSeat and adapters are sold separately (the sticker price is only the beginning), and it is expensive. Skip it if you have true twins from day one — you can only run one bassinet at a time in the newborn stage, so twin-newborn parents are better served by a side-by-side or a two-bassinet setup. But for two-under-two arriving a year or two apart, nothing else adapts this gracefully.