I hear ya! I have ridden the subway with my 13 mo old since her birth and have gone through many options. here are my findings:
Cheapy umbrella strollers are good if you want to carry her up all of the stairs while she's still in the stroller. They are light and least bulky. - still takes some acrobatic skill and weightlifting.
Your bugaboo isn't as bad as you think, because it has good sturdy wheels that can roll up and down those stairs like a furniture dolly.
An Ergo carrier is often easiest because you can just strap her on, but then you are also carrying her the whole way on your trip, add some bags and youv'e become a pack mule.
All options will require a work-out, but there is often a kind stranger at the stairs who will help you carry the stroller - usually another city mom who has been there...
You can also plan your trip ahead of time by going to the MTA website and getting a list of wheelchair accessible stations - these have elevators and ramps, so it's easier for strollers, too - I often walk a little further just to use one of these stations - a trade-off that can be worth it!
Also - If you ever have to take a bus, avoid strollers altogether - They do not allow them on - unless folded and carried, so you have to carry child in one hand, stroller in the other, and any bags and purses -- just not enough hands! - Use a carrier like the Ergo or Baby Bjorn instead (Ergo is easiest on my back).
Hope this helps! Happy trails!