Beezy

The Joolz Aer for sure! My 71 year old mother in law uses it regularly while watching my baby. She can lift it up and down our front steps and in her words "I love this stroller and wish I had it when my kids were babies." We also have the Cybex Beezy which has a very similar fold, cheaper than the Joolz Aer, slightly heavier but my MIL is able to lift that stroller too. Both strollers have great suspension and we've traveled the world with them on various terrain.

I have the Joolz Aer and I love it. I've had it for 4.5 years and it has traveled the world with us. It is lightweight, sturdy, has a one hand open/fold, great suspension, fits in the overhead bin or airplanes, and I now that I have two kids and use it with the footboard that my toddler rides on and baby sits in the stroller. I also have the Cybex Beezy which we also use for travel and we like it for the same reasons we like the Joolz Aer (I prefer the Joolz Aer and my husband prefers the Cybex Beezy so we each use one for each child when we travel).

If you're haul fit up and down 4 floors regularly, absolutely get something compact that it easy to fold/unfold and lightweight for carrying. Probably a bonus if it comer with a carry strap you can put over your shoulder, or you can add one yourself. I really like my cybex Beezy. I originally bought it for travel, but it just became my everyday stroller and it handles rough terrain well for being so small and compact and I think it works well on cobble for a compact stroller, but it isn't as smooth as something with a more robust spring system. 

If you are folding it up often, I would steer away from strollers with attached bassinets because those will generally be much more cumbersome and difficult to haul around while also carrying your baby! My goto stroller for easy portability while still being able to shop is the Cybex Beezy, because I can easily fold or unfold it with one hand with some stuff still in the bottom basket. We used it extensively for farmer's market shopping, travel, and the park. It doesn't fold completely flat, though! Almost, but not quite.

I use the Cybex Beezy. It’s a travel stroller so it’s slim and light. It even fits down the aisle of a plane and into the overhead compartment. I’ve found it’s great for outings like Disneyland too. It folds up quickly and easy on the tram. I’m a single mom so I need something that works quickly as I don’t have backup. Have fun!

I’m a single mom and my son and I have been traveling since he could first walk. I take a travel stroller (Cybex Beezy) that folds in the overhead bins on a plane. For me it’s helpful to cart my son across a large airport and to contain him a bit. My son is now 4, but it was especially important when he was 2! Good luck!

We went with Uppa baby vista v2 complete system as our primary stroller and stokke YoYo as travel stroller. In the process I had multiple trial & errors, exchanging etc to find what meets our needs. My learnings: 1. Don’t buy stroller too early, you want to be within exchange window once baby arrives and you use it on baby only to realize it’s not what you want. Pre-baby moms like me choose light weight medium stroller but the moment baby’s here, your feelings can change. You may want the sturdiest and comfiest one for baby over your own comfort. Happened with me so switched from nuna to UP vista v2 2. Terrains in your neighborhood and lifestyle are big consideration factor. If you hike, go on trails or plan to take stroller on uneven surfaces then heavy built stroller. 3. Safety considerations: Some stroller seats are harder shell while others are thick cloth with padding. I can’t imagine someone hitting stroller with vehicle but I once had a child lose control of bicycle and hit the stroller from side. LO didn’t feel anything other than a bump thanks to the hard shell of our seat. 4. Bassinet: Depends on your need, if you plan to be out walking the first 3 months more than an hour at a stretch then bassinet becomes useful. I was able to lead my usual pre baby lifestyle with frequent outdoor time because of bassinet. If you plan to mostly rest and recover with less outdoor trips then car seat attachment works. It does take space in trunk. 5. Baby’s size: If you have a heavy baby (not just chubby but actual 90 percentile above one) the light weight strollers aren’t useful for longer period. Example: I tried cybex & doona as travel alternative but both failed. Cybex travel stroller was so flimsy and would seem like it will break if baby tried to fight the stroller. Doona though it says 12-18 months, I borrowed for an international travel from a friend who has 12 months baby. My 9 month wasn’t fitting as he was big and it felt his shoulders were getting stuck. Travel strollers are best bought only once baby is here and the neck stabilizes.

Stroller/car seat combos tend to be pretty low when on stroller mode. Like u/diatho said, get a travel system. Our first one, my wife splurged on a Nuna and the stroller extends to accommodate taller peeps. Fabric was superb and easy to grab and go. The carseat uses an adapter for the stroller but is just one piece. It is very expensive though. With our second one, we ended up getting the cheapest Cybex system and it works out well. Only thing I don’t like is the you have two adapters for carseat and another two for the bassinet. It can somewhat accommodate tall peeps since the handle swivels in varying degrees. I heard good things about Graco and Chicco as well but my wife hated the texture of their fabric. And since they’re roughly the same price as the cheapest Cybex, we just went that route instead.