Soil components can vary significantly between different landscaping companies. What one company considers topsoil or black dirt can be very different from another. I would start by asking the company if they have a specific soil they recommend for vegetable gardens. Then ask each company if they amend their soils by adding compost or composted manure. Some landscape supply companies can even provide basic soil test results. Most landscaping companies have a topsoil blend that contains compost, specifically meant for vegetable gardens. While you can get topsoil and blend it yourself with compost or composted manure, you might quickly regret that decision. Hand mixing this much soil can be very time consuming. 

I would also recommend visiting the landscaping companies first to see their product. Be on the lookout for debris, trash, and plastic contaminants. Don't be tempted to get the cheapest soil you can find as it's often filled with a lot of sand and small rocks.