The E17 to Brussels, the E403 to Charleroi
For Brussels Airport (Zaventem), the route from Kortrijk, Harelbeke and Waregem follows the E17 towards Ghent and then the E40 to Brussels and the Ring. From Ypres you join it via the A19, from Roeselare and Izegem via the E403. It is a substantial drive, and at rush hour traffic can back up around Ghent and on the Brussels Ring. Your driver builds in plenty of margin; you choose the pickup time.
Flying low-cost? From the south of the region, Charleroi is well worth considering. The route heads south via Tournai and Mons, steering clear of the Brussels congestion. Liège, Eindhoven, Schiphol, Düsseldorf and Cologne Bonn are available too. The price table on this page shows the fare from your town to every airport.