Hmmm...Cuisine, for one thing. I know it's a cliché, but generally speaking, I vastly prefer the Belgian food over Dutch food. Both for top cooking, as for fastfood. And because I'm not going to take the easy route, I'll include chocolate, and the very obvious, beer, here.
Secondly, our educational system. It has its drawbacks, certainly, but I've known friends in both, and I tend to prefer the way it's handled in Belgium - universities are given funds according to starting students in stead of for graduating students, for example, and tuition fees are much lower. Again, so as not to cheap out, I'll throw in the bigger multiculturalism and multilingualism. Practically all Flemish know at least French and English; many know either German or another language as well.
Thirdly...hmm. Though I do prefer the Dutch way of approaching things, which is more bussinesslike and oftentimes seems cooler and more efficient, sometimes I do really appreciate the Belgian - and this mostly in Wallonia, really - joviality and openness to strangers. It's different from the way the Dutch are open; and there's a certain...Bon-vivant thing going on, often. It can irk me greatly occasionally, and it is once again quite clichéd, but still.
And gruebeard: "nul vijfhonderd" means "zero fivehundred". The rest's just my number :-P