Black & White -vs- Color

I find that I often struggle with the decision to take shots in color or in monochrome. Sometimes the photo just works better without color. For example, look at this Civil War era iron smelting furnace. In color, you see the different colors of the rocks, the green of the trees, and the sharp white of the cap that the National Park Service placed on top.Now look at the black and white version. Same shot composition, just missing the color. I like the simplicity of the shot - no green grass or trees to pull the eye away from the furnace and your imagination can place the furnace into the past.
As a quick history lesson... This stack is what is left of the largest iron creating furnace that existed during Civil War times. There used to be a bridge/catwalk that allowed carts to dump the ore into the top of the furnace. The whole mill was built up around this area and stood several stories high. The mill was known for producing the highest quality iron, and that iron was used for many purposes before, during, and after the conflict. One of the items that was produced in large numbers during the Civil War were cannons. Which brings us to the second set of B&W -vs- Color photos.

Again, these two shots (pun intended,Ha!) of the cannon were taken from the exact same location, seconds apart. I can't decide which I like better. The green of the grass seems to add to the picture, rather than take away as it did in the furnace picture. The color of the grass also works well with the patina of the cannon barrel. To me, the black and white of the cannon seems to be stark and cold. I guess the overall decision comes down to what I'm trying to convey through the shot.

What do you think? Do you prefer color or black and white? Does it depend on the photo subject? I enjoy shooting both in color and in B&W, so you'll see a mix as the posts continue.