That was by far the hardest choice I had to make. I really like Mystara, certainly my favourite "kitchen sink" setting. But... Al-Qadim is excellent because it gets the "feel" of an Arabian Nights setting about as well as it could be done.
I suspect Rokugan isn't that familiar compared to Kara Tur. Most Realms fans have probably heard of the latter, while the former only really appeared in the 3.0 Oriental Adventures book; and almost as an afterthought there. If it's down to Fantasy China/East Asia being more popular than Fantasy Japan I'd be pleasantly surprised.
