Source: https://www.reddit.com/r/jurassicworldevo/comments/128qhre/updateand_rework_maps_size_chart/
Reddit user u/86karlos made this nice chart showcasing the size of maps in JWE 1+2. It is a very nice reference I like to use and the data presented looks to properly reflect the size of the maps in the game.
The biggest maps for sure are the square maps at 6.25km², they are the largest maps available in the game and provide the most room to build your parks on regardless which biome you choose.
The biggest non-square map is the San Marie Bay -Expanded map at 3.78km².
The biggest non-expanded map is the Sierra Nevada map at 2.55km².
The not-expanded North California map is the biggest non-expanded map available without DLC. So for a time, this was the go-to for more room, but DLC and updates provided much larger options since then.