I have an idea for a map I wish to create, but I am not sure whether I should forge it on foundry or sandbox. On foundry, the items will look aesthetically closer to the feel I want (Think shantytown). On sandbox, I'll be able to spread the level out, and have vehicles. What is your opinion? Note that I don't have the mythic map pack yet, so if I were to decide to forge it on sandbox I would spend more time in the planning phase than I normally might.
No Mythic yet, and no release date announced = build on Foundry. If Mythic comes out and you like Sandbox better, you can always rebuild it in a quarter of the time it took you on Foundry.
I'm starting to realize I like Foundry better than Sandbox. If you're going for a city sort of feel, definitely go with Foundry. You can still have vehicles on Foundry if you make a vehicle friendly map.