Well, some of them won't be available much longer - at least not from Lego and official shops. You'll be able to buy them off ebay, but they'll get more expensive once they're out of stores. If you are thinking about buying more of them in the future, I suggest to buy the Parisian Restaurant or Assembly Square (AS being the larger and more expensive one of the two) before they go out of production.
If you really only ever want one, my personal favorite (of the ones still in stores) is the American/Downtown Diner. It's so charming with it's bubblegum colors and funny interiors. Also, since this one is newer, you'll be able to get deals on it. I bought mine 25 percent off.
I'm also in love with the 50s theme, though I hate the more industrial look of the Corner Garage (first modular I haven't bought in years). If it's more like the Diner, I'm all for it. Petticoats and ponytails, convertibles and rollerblades, and the architecture and colors to go with it - it's brilliant fun.