2 and 3 are your best ones- good focus, a good level of abstraction without being totally ambiguous, and good move with the black and white.
#1- flowers are boring. We've all seen that shot dozens of times before. Bring something different to the table or don't bother.
#4- I don't really know what you're taking a picture of. An incoming train? The convection currents distort any picture you're trying to get at that distance.
#5- interesting idea, I think it could be better composed though. Maybe arrange yourself so you can get a shot of the "real" engine car and the small engine car?
#6- the shallow DoF makes it hard to get what you want in focus. For example, since you're at an angle the first couple letters of "Electronic" are blurry. This in turn casts doubt on what you're trying to accomplish with the shot.