Have a close look at the advanced features on them. The ROG GT routers are probably the most feature rich, then ROG GS, then ASUS RT. Some of the advanced features around things like QoS really need to be on the router that faces the Internet (the one directly on your ISP line / modem / etc). So, it may be best to have the GT as primary router and directly on the Internet, with the others as AiMesh nodes/repeaters. Directly connecting the mesh repeaters over Ethernet, back to the primary, should give the best overall performance.