Orly to Belgium-train out of Paris or car rental?

I suggest Arras as a centre for WWI sites and an interesting small city on its own. If you are travelling after a long overnight plane flight, public transport is a easier and safer way to go. The fast train from Gare du Nord to Arras is about 45 minutes and there is hotel accommodation near the station. http://www.explorearras.com/?lng=en

I would also advise not making that drive on the heels of a long flight . Train to Lille where you can pick up the car , and it is then a short drive up to Ypres and some of the WW I sites in Flanders , We did this in 2015 and then drove west through Northern France stopping to see Amiens , sites in the Somme ( WW I ) , and Compiegne , before dropping the car at CDG , on our way into Paris . Unfortunately , we missed Arras , which is quite worthwhile , as I understand .

My two cents: if you're going to be renting anyway, why bother with the hassle of getting across Paris by RER to Gare du Nord)? I would just drive straight from Orly. Its way out of town, outside Le Péripherique, and easy freeway driving the whole way to Lille, Bruges, Brussels or wherever you're going to be based.

Darrenblois, the drive may be straight forward, under normal circumstances. But driving while jet lagged is neither normal nor safe.

Have you ever experienced Belgian drivers?

I typically take public transport until I need the car. For me it saves mental energy that I can use later in the trip. I drop the car off as soon as I no longer need it for the same reason.

Thanks for your inputs, good points all. Having been in Brussels, I've seen the driving but I've also driven throughout France, and from Venice to Rome in addition to Chicago, NYC, LA, and DC.