I'm a baby wearer, but my first outing with ds in sling and dd in stroller ended with me in tears. It is really hard to control a toddler when you have a newborn in the sling. I got a bj city mini double and it's changed my life. I like the way both babes can be protected from sun and weather with adjustable hoods...both can sleep with reclinable seats, and honestly it's easier to push than the stroller especially when the baby in the sling gets heavy (ds is 9kg at only 4 months).
I am a big walker and I love my double pram! If I had th cash I would have got a city select, but we got our city mini double cheap from eBay because I wasn't sure how much I'd use it.

Oh and fwiw dd is 30 months and I can't see our pram use slowing.