Wow - I wish I was that lucky. I've never been to those places you mentioned. However, I'm not sure I would pick Seychelles if you like nature and architecture. In my opinion Seychelles is more of a resort island for one to rejuvenate. Again, I may be completely wrong and misinformed.

However, since you're already in that area of the world, you probably are better off visiting South Africa. However, if you are up for a bit further - Halong Bay in Vietnam is breathtaking. That's what I call nature.