Having spent many years using strollers, here's my take:
Umbrella strollers are cheap and lightweight, but don't roll well. Besides the hunched back of the mom and the fact that they're not good for babies under 6 months (lack of back support), they are very hard to push. As the child gets older and heavier, they also get heavier and harder to work with. They're very useful if you have a car and can keep one folded in your trunk- they take up very little space and are easier to push on inside surfaces, like in the mall.
The reason you see parents with SUV type strollers is because they are really easy to push- they are built with rolling easily and on different types of surfaces in mind. They're great for jogging, etc.
Having lived in a major city without a car, I (and most of my friends) didn't use either of those. If you need to get around with your child, SUV type strollers are a real pain. Lots of them don't fold easily, take up more space than is often available on the sidewalk, get in the way while shopping, etc. They're really not convenient in the city. There are mid-level strollers that combine decent suspension with a more moderate size and those work the best. They're not too heavy to bump down the stairs, roll nicely most of the time, have some storage for shlepping and don't get in the way as much.
Also- in my city, the rule was strollers get folded unless you pay an extra fare. When it was too hard for me to fold the stroller, (sleeping baby, too many bags, too short a ride, squirmy kid) I was happy to pay an extra fare and not have the hassle.