If you want to stick to just one, I would go with the Nutmeg Paraty (I have the Nutmeg and it is one of my favorite bags hand down), although the sm/med Marcie in Whiskey is gorgeous, too. Marcie and Paraty are my favorite styles, but if I could live with only one, it would be Paraty for its ease, comfort on the shoulder, and classic look. It's so unique, nothing else looks like it.
If you do go with the Marcie, it also comes in a color called "Tan," which is more of a British Tan color and is a gorgeous option - a little lighter than Whiskey and less Brick/reddish in color. I think I last saw the Tan in the sm/med satchel at Neiman Marcus, although it not available on NM online.
Either way you can't go wrong, but my vote went for Nutmeg Paraty.