Both have pros and cons. It usually depends on how you plan to use them and how often you open the windows. Casements tend to seal better, though.

That exact choice came up during my renovation. I initially leaned toward sliding windows because they seemed easier to maintain. However, after visiting https://windowtechcanada.ca/ windows and doors and speaking to their consultant, I ended up going with casement windows for most of the house. They explained that casements have a tighter seal due to how they close, making them more energy-efficient in cold climates like ours. The hardware on newer models is much more durable than it used to be too. They also swing open fully, which has helped with ventilation in the kitchen during cooking. The sliders were fine for smaller rooms, but for main living areas, casement offered more control and efficiency. Installation was fast, and everything came with a decent warranty.