So, to the question of whether to bring a stroller or not with you for your trip to Hong Kong, here are the things you must consider:
1) How old is the child?
Personally, I think an infant will be better off being worn in a carrier or sling or pouch. This way, you don't have to remove them from the stroller when necessary.
For toddlers up to 3-4 years old, strollers may be the best way for you not to lose them in a crowd. Plus, they will still really complain about long MTR walks (where everyone is in a hurry and all you see are people and exits). They don't mind the walk so much if you're not in a hurry and they can stop to check things out along Hong Kong streets.
2) Who will be in charge of the stroller?
Will you have a designated driver for this one? Who will it be and will he be amenable to keep folding and unfolding it when you ride buses, or to carry it down MTR stairs or Ocean Park steps if you cannot be bothered to look for the elevators and special ramps?
Ocean Park has a lot of ascending or descending terrain
3) Where will you be going and how do you plan on getting there?
If you don't intend for the kids to tag along when you brave shopping districts, and would only really need them at amusement parks, then just rent at amusement parks.
If you're going to so many places in a day, and boarding the bus many times, a stroller may prove to be a hassle since you have to fold/unfold it and stow it away properly. You may also have to worry about where to park such things in the general Hong Kong area. Plus, since you're likely to also put your things in there, you may inadvertently leave a valuable behind when you're parking it aside for a show.
But if you're say, staying in the Nathan, Kimberley, Cameron, Granville area and intend to just shop there, and keep utilizing the MTR, then a stroller will help in keeping the "Are we there yet?" and "I don't want to walk anymore." moments to a minimum.
4) What is the purpose of your HK trip?
If you're after visiting as many sights as possible, then you'd probably be in a hurry to get places and a stroller will slow you down. But if it's a leisurely trip with the purpose of delighting the kids you are with, then a stroller would serve you well as you visit parks too.
5) What kind of stroller do you have/plan on bringing?
If you're like us who own a heavy duty one with shocks and a really sturdy body, it just may be impractical and just more work to bring it along.
If you own a lighter model (most umbrollers are) or can borrow one, then taking the stroller up and down some areas may be easy as pie.
* Other notes/tips:
~ you have to carry strollers up and down MTR stairs but there are elevators within the MTR station and spaces inside MTR cars for strollers and wheelchairs
~ Hubs felt we'd have felt bad about a new one getting roughed like ATV Tires at Ocean Park and fully appreciated their heavy-duty rentals.
~ even 6-year olds will benefit from a stroller at Ocean park becase it's really a huge area to cover on foot. However, a stroller may not be maximized as much at Disneyland since the attractions are closer together so the child will be more likely exploring on foot.
~ for those willing to push and carry (up and down steps), a stroller will also accommodate your backpack and shopping as well as provide a place to nap for your tired toddlers/kids
~ there are designated parking spaces for strollers at Disneyland and Ocean Park, just be careful not to leave any valuables (or the umbrella) behind
~ Strollers/wheelchairs may be rented at Hong Kong Disneyland (HKD60/day with HKD100 deposit; HKD200 deposit if weather forecast suggested rain to cover the stroller rain gear) and Ocean Park (HKD40/day with HKD60 deposit). You get the deposit back upon returning the strollers and you get to keep the name card (a sort of ID attached to the stroller, with your child's name written on it) as a souvenir.
~ Strollers aren't allowed inside the Ocean Park cable car but there are special lanes and allocated area for people travelling with kids/strollers inside the Ocean Express (tram).
Kids can remain in strollers inside the Ocean Express and watch the show from the ceiling screens from there.
Ultimately, it is still your call whether to bring your own stroller or just rent from there. People used to be able to rent strollers from YWCA-HK too but nobody responded to my e-mail. You can also shop for umbrollers there for as cheap as HKD250 and dispose of it later if you really don't want to actually bring a stroller and check it at the airport.