A good half sheet pan is heavy-gauge aluminum, thin cheap pans warp in a hot oven and bake unevenly. Buy at least two so one can cool while the next batch goes in.
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Nordic Ware
The most recommended baking sheet for a reason, heavy-gauge aluminum that resists warping and bakes evenly, at a price that undercuts most competitors. It has no nonstick coating, you'll want parchment or a silicone mat under sticky bakes.
USA Pan
Adds USA Pan's silicone-based Americoat nonstick finish over aluminized steel, so release is easier than the bare Nordic Ware. The coating means you should hand-wash rather than scrub with abrasives to protect the nonstick surface long-term.
Chicago Metallic
A commercial-grade uncoated aluminized steel sheet, thick enough to resist the warping that plagues cheap cookie sheets. It's a flat cookie sheet with only one or two rimmed edges, not a full rimmed sheet pan, check the shape matches what you need.
Wilton
The cheapest reasonable entry point, and buying two at once solves the batch-baking problem immediately. Thinner gauge than Nordic Ware or USA Pan means more risk of warping at high heat over years of use.
Williams Sonoma
Heavy-gauge steel with a durable gold-tone nonstick coating that browns cookies evenly and releases cleanly. It costs multiples of the Nordic Ware pan for a similar core job, buy it for the coating and finish, not because it bakes fundamentally better.