An eyeball is just a way to adjust the direction a reflector bulb is pointing, as if you were shining a flashlight in one direction or another. With wall-washers, most of the light bounces off the interior of the trim and comes out sideways so the focused beam is broken up and diffused, softly lighting a larger area instead of intensely lighting a smaller one.

PAR30 bulbs are halogen, typically be slightly cooler in color, produce more light per watt, are more crisply focussed, and last longer. BR30 bulbs are standard incandescents; they're slightly warmer-colored, more diffuse, less efficient and burn out sooner.

Another point is that the eyeball may produce a more dramatic effect on the wall. Think of it as an upside-down Y. The wallwasher is for generally washing the wall. The dramatic effect you normally see is from eyeballs because of the Y effect on the wall.

It is just a matter of choice and what you are trying to light. If it is art work, you need to be sure that the light is getting to the area. A good way to check what you want is to take the light bulb you intend to use and put it in a lampholder. Get on a ladder and hold it up to where the recessed light would be. You can then see what the effect will be on the wall. Everyone can tell you what they know, but I think everyone needs to see it if possible.

jon1270 is right about the bulbs. I would only add to make sure that the recessed lights you select can take either of them. There are fixtures that will take both. Also, you can elect to use the Neodymium (true daylight) bulbs in place of the BR30. They are, however, more expensive and don't last much longer. But they do give you a wonderful rendering on colors, if that is your main concern.