Either is worth a weekend, and we've done both. I've twice done done Bruges in a day trip, one of them via Enfield when I took my dad. Bruges is a lovely place but there's probably more to do in Brussels. There's the Atomium, Grande Place Mannekin Pis, a comic-strip 'cartoon' museum. Rue des Bouchers is good for the restaurants, there's a good fish one up there.