We have 2 strollers that we take with us (we have 2 little ones). One is a bigger Graco travel system stroller (minus the infant car seat), the other is a Chicco umbrella stroller. On the busses we collapse them and carry them on. This can be tricky when carrying an infant and 2 year old, but we do it. On the monorail we bring them on with the kids still in them, esp if they are asleep. But we push them all the way in to make room for others.
Bring which ever stroller your child prefers. I know that my girls are big on shade and need to have the stroller lean back for nap time.