It really depends on so much. When DS was born, I didn't have a stroller, and planned to BW him exclusively. At 3 mos, he refused to be worn, period. Not in the Moby, not in the RS. I bought a 2nd hand (high-end) stroller at a consignment shop and I've been perfectly happy with it. I was able to start wearing him again around 5 or 6 mos, but still used the stroller for things like trips to the grocery store. We live at the top of a hill, so having to climb it with him in the carrier was a pain anyway. I do live in a big city, and public transportation sucks, but the two times I've taken him on the bus, I was glad for the stroller - trying to keep my balance in a moving vehicle with him strapped to my back is a daunting prospect (getting a seat is a laugh). The stroller has been handy for lots of reasons - going to the farmer's market and being gone for hours because I decided to take a side-trip through Chinatown... I couldn't do that with a carrier. Taking him to the gym, and leaving him in the stroller in the childcare until he asks to get out - it's his personal space bubble. Or taking a walk to the post office to ship packages and just taking our time because it's a beautiful day.
Because at 16 mos, DS is already almost 30 lbs, and over 31 inches tall. I do still wear him on occasion, if he's fussy or if the stroller isn't practical, but by far my preferred carrier is my onbuhimo, an Ergo would never fit me. DH prefers wearing him to the stroller if they're just going on a walk, but he prefers the half-buckle tai (and I have to put it on him still). I would be far more housebound than I am without the stroller just because I don't have the ability to wear him for long periods as heavy as he is.
And just this morning DS declared his independence by climbing into the stroller and saying "go walk" and when I asked him if he wanted to go, he said "let's go".