You’ll learn quite a lot regardless of your choice. Business school is more practical/pre-professional, while Econ will be(come) more theoretical as you progress.
In business school, you will (or should) learn what is necessary to start and manage a company. Your core courses will likely include courses like Financial & Managerial Accounting, Finance, Marketing, Economics (micro and macro), Operations Management, Business Law, International Business, Organizational Behavior, and IT Mgmt.
Why are these things important in starting and running a business?
Finance - You need to be able to raise funding for your company and evaluate and manage equity and debt
Accounting - You need to be able to track the fiscal health and performance of your company and balance the books.
Marketing - You need to be able to sell your product or service: create a product with sellable features, choose a market to sell it to, choose a location or means of sale, transport the product to that place, promote the product or service, etc.
Economics - You need to know the laws of supply and demand – equilibrium price, how changes in price or quantity are likely to affect demand, etc.
Ops Management - You need to know how to be effective and efficient in your core operations.
Business Law - You need to understand basic contract law.
International Business - Especially if you are in a global company, you need to understand how international forces like trade and currency can affect your firm.
Org Behavior - You should understand the basic types of firms, company cultures, and how HR generally functions.
IT Mgmt - You should understand how to set up a basic IT infrastructure, how to evaluate IT decisions, etc.