Keith,
I've seen all three courses, Morfontaine, Fontainebleau, and Chantilly, and here's my opinion.
Any one of them is worth going out of your way for, but I would choose Morfontaine, Fontainebleau, and Chantilly, in that order.
Chantilly is the flattest, and for that reason I believe the least interesting. It relies too much on cross bunkers for strategy, which gets repetitive after a while. Also, it is not built on the depths of natural sand that the other two courses have, so it is a little softer and slower. I played it in wet weather, and the greens were slick as you get in France, but the fairways were so muddy with earthworm casts that they were unplayable in some areas.
Fontainebleau has a magnificent piece of ground, and the most ingenious routing to take advantage of the natural terrain, but I believe it is being mis-managed. Not in the day-to-day maintenace, but in the long-range, strategic sense. Trees are overgrown and encroaching the fairways, so if you miss the short grass at all you have some over-hanging branches to deal with. I don't think it's what Simpson had in mind when he laid it out. It reduces the route to the hole to one. There is the pre-requisite sandy soil, strewn with boulders, and the broom and heather is naturally invading the unmaintained areas. You need to carry the vegetation to reach the fairway in on a number of holes, but not enough is done to encourage these plants to take their rightful place in the lines of play and to influence strategy, not to mention appearance. There are a few absolutely brilliant green complexes. I think it was #14, a par 3 with the most effective false front I've ever seen, that comes to mind.
Morfontaine was truest to architects intent, I believe. It is built over 9 meters of pure sand, so it's got enviable drainage, and Simpson could get away with murder putting in things like punch-bowl greens and fairways that wouldn't work elsewhere. The heather is carefully maitained in its rightful place, forcing you to think about carries and shot placement. The trees are encroaching, but it's still open enough to offer some interesting choices. The green complexes are spectacular, some of the most severe undulations on this earth. The pine forest all around ensures an atmoisphere of serenity and solitude, especially as it is only lightly played. The day I was there, I saw one other group of players.
All three courses are maintained to the highest French standard, which is to say middle-of-the-road for people who are used to States-side conditions.
I was politely welcomed, generously accommodated, and treated with the utmost respect by the management at all three courses. People whose experience does not match this reception may be approaching these clubs in the wrong way.