I can't see how an A Class (prestigious compact family car) compares to a Forfour (simple small car). The Forfour is a cute car, but it isn't half as special as the other Smarts, it's an ordinary small car. I don't know much about it though.
I better keep to myself what I think about that Civic...
Anyway, what do you need/want from the car? What's important to you (size, internal space, ride comfort, accessories, handling, performance, style, etc.)?
(BTW - in my opinion, the A Class is Mercedes-Benz's best car nowadays. It's their only special car, the only one that innovates, the only Mercedes I like.)