What are the Pros and Cons to each one? Most of the time I am making vegetable soup.
Commercial stock or broth products come in several categories. Of the ones you ask about:
Bulky, but ready to use. May be the highest quality product of the three you asked about, with the best flavor. Especially low salt versions contain less salt than the cubed or powdered alternatives.
Contain lots of salt. Must be dissolved in hot water before use. May not be as high a quality product as canned. Requires little shelf space. Often inexpensive on a per serving basis.
Essentially the same as cubes, but not yet pressed into cube form. Somewhat easier to dissolve than the cubes.
While you did not ask, concentrated stocks are also available on the market, which are almost like a jelly that you can add to thicken and enrich sauces, or reconstitute with water to use as a soup base. These tend to be marketed at commercial kitchens, and may be a higher quality product than some of the others.
It's hard to generalize them since within each category there are vastly different qualities.
Read the ingredients list carefully.
I have a favorite option, it's a concentrate or "base", like SAJ14SAJ mentioned. Costco now carries it, making it also an inexpensive option - Better than Bouillon, the organic, reduced sodium variety. I almost always make my own broth, this product is great for stretching homemade or enriching it. In a pinch, it's even OK just mixed with water. It was included in America's Test Kitchen tasting test of canned broths, it tied (or almost tied) Swanson's canned broth for 1st place. Other answers have very well covered the pros and cons of each type of chicken broth product, this one just happens to be my favorite of all of them. All pros, no cons.