But I think 3 sites for Pueblo culture, Chaco/Taos/Mesa Verde, are too much better choose one, and my opinion is Mesa Verde for its more complete archaeological findings on ancient people's agricultural, irrigation and architecture.
"Chaco hosts the densest and most exceptional concentration of pueblos in the American Southwest." - wiki
"Chacoan developers assembled 15 major complexes which remained the largest buildings in North America until the 19th century." - wiki
It was a significant trading center with a large population. This network of roads and connected components allowed contact with peoples along the coast of California and as far South as Mexico City. Mesa Verde is indeed spectacular, but its difficult to argue its importance compared to Chaco.
For myself its very hard to select one (maybe 2) of these sites: Mesa Verde, Chaco, and Taos. Thats because they are actually very different and taken together tell a far more complete story. Let's also be honest, there are likely 3-5 additional Southwest Puebloan (Sinagua/Hohokam)
sites worthy of inscription. If I had to select only (2), I would grudgingly go with Mesa Verde (Iconic) and Chaco (Massive complex and for importance), though its a shame to leave out Taos Pueblo which is unique and special for its own reasons.