Two sides of one region: via Antwerp or via Brussels
In the Waasland, around Sint-Niklaas, Beveren and Lokeren, the quickest way to Brussels Airport usually follows the E17 towards Antwerp and then the E19 to Brussels. From Temse and Hamme, you can also cross the Scheldt bridge to Bornem and join the A12. Because the Antwerp ring road often clogs up at rush hour, your driver picks whichever route is flowing best at the time.
In the Dender valley, Brussels is closer. From Aalst and Ninove, you reach the Ring and Zaventem via the E40 or the main roads. Dendermonde and Zele sit in between: depending on the time of day, the route runs via Aalst or via the A12. For you, it makes no difference: the price per town is fixed, whichever route is taken.