Pick Petronas skybridge if you only buy one ticket — you walk between the towers at 170m and the view of KLCC Park below is iconic. KL Tower (Menara KL) gives a better panoramic city shot including the Petronas silhouette, and is usually shorter queues, but tickets still run RM40–80 depending on deck package. Skybridge alone is roughly RM35–85 by package — book the cheapest skybridge-only slot online. KL Tower at sunset is romantic; Petronas is better for kids who want to brag they stood on the bridge. Free alternative: KLCC Park ground level photos at the fountain show — no ticket needed.
Petronas skybridge — you're IN the towers. KL Tower you look AT them. Pick Petronas if you only do one.
Atmosphere 360 restaurant at KL Tower is pricey tourist food — skip unless dinner is the point.