Hey, as a mom who's been lugging strollers up three flights of stairs for two years now, I totally get the struggle with a small apartment and no elevator. You want something that folds up quick with one hand, right, while you're juggling the baby and maybe a bag or two. Aim for ones that weigh around 12 pounds or less and and practice that fold in the store until it feels second nature. Durability wise, check for sturdy frames that don't wobble when you push down on them, and wheels that handle cracks in the sidewalk without rattling your teeth out.
For travel, especially buses and planes, a compact fold is a lifesaver, something that stands on its own so you can park it without it flopping over. I've found that locking front wheels help on uneven ground, and a good brake that engages easily keeps it from rolling away on a bumpy ride. To make it last, wipe down the fabric regularly and keep the mechanisms clean from dirt buildup. Oh, and a higher weight limit ensures it grows with your kid through those toddler tantrums. Works great.
