For me it definitely has to be Harvest. Love the fan service of the map’s location, it looks beautiful, and looks like it lends its self well to a number of different objective games. Looks to be an all around classic Halo map.
Shatter and Wreckage to me have a lot of the same problems the other “vehicle-friendly” maps in the game already do. Yea in terms of square feet they are quite large, but there are so many narrow corridors and sightline blockers that using vehicles almost feels claustrophobic. 343 seems to have a crazy obsession with just throwing giant rocks everywhere to make these big maps feel confining.
And also Wreckage, and to a lesser extent Shatter, have WAY too many different routes, caves, and alternate pathways. It makes the flow of the map somewhat convoluted. Take a map like Ragnarok for example. It’s a large open map (no giant rocks every few feet) and essentially has 3 different routes you can take (middle, turret side, and pelican side), but has one or two extra small channels you can take as well. That way you have some alternate routes you can take but overall there are so few that the map flow is still very focused and readable. That’s how to do a large scale map.