A glider is one of the few pieces of furniture you'll use every single day, often for months at a time. Before you fall for a colour or a shape, sit in it. Your feet should rest flat on the floor, and your arms should land comfortably on the armrests without you having to reach or slouch.
Size matters more than people expect. Measure the corner of the room where the chair will live, including space for the glide itself — most gliders need a few extra inches front and back to move freely. A chair that's slightly too big for the room will feel cramped no matter how comfortable it is.
Look closely at the glide mechanism. It should move in one smooth, continuous motion, not in small jerky steps, and it shouldn't squeak when you rock at different speeds. A well-built glide is quiet even after years of daily use — that's worth paying attention to at the store or in reviews.
Finally, think about the fabric. A tightly woven, easy-clean fabric will hold up far better than a delicate one, especially if the chair is going in a nursery or a busy living room. Darker, textured finishes tend to hide everyday wear the longest.