Without a doubt the spray foam will be more solid and have everything "locked in".
We spray foamed the walls in the shop when we built it, which was nothing more then a wooden pole barn with steel siding. The foam job sealed everything up, and made the whole building more rigid and way more quiet in the wind/weather.
We had no issues with chemical off gassing. We let the walls sit open for the time they recommended. And now they're covered you wouldn't be able to tell, especially with the chemicals that are present in your typical shop.