Three Working Definitions of Knowledge

Knowledge is a little more difficult to pin down than truth. Understanding what knowledge is begins with its definition and one's theory of knowledge is guided by this definition. Remember, "knowledge" is just a word... not a metaphysical thing that's "out there somewhere." We ought to select a definition that's useful to us and easily communicated.
Here are the three major definitions I have ran into:

Absolute Knowledge

(Championed by Immanuel Kant & Philosophical Skepticism)
Knowledge is only that which we know to be true with absolute, 100% certainty. I haven't really found this definition to be useful, since (under this definition) no one "knows" anything. Knowledge is an impossibility; metaphysically unreachable for any mind with limited knowledge. This is easily demonstrated through a syllogism:
Premise 1) Human minds have limited knowledge.
Premise 2) What one does not know may render prior knowledge incorrect.
Conclusion) Humans can't know anything.

Kant readily accepts this conclusion. This doesn't lead me to think I can never know anything. Instead, it leads me to look for a better definition. Perhaps a more useful one?

Contextual Knowledge

(Championed by Ayn Rand & Objectivism)
Knowledge is only that which we know to be true with absolute, 100% certainty as framed in our knowledge context. This definition is a little more difficult to grasp and requires further explanation.
This model disregards that which is outside our knowledge and evaluates certainty only in the context of existing knowledge. For example, in the context of Newton's observations, Newton had certain knowledge that F = ma described the relationship between force and mass. In the context of Einstein's observations, Einstein had certain knowledge that F = ma was wrong and that  described the relationship between force and mass.
According to this model, both men had certain knowledge about force in the context of all their knowledge. I find this aspect of the definition difficult. I have found it a complex en-devour to communicate well with others using this definition of knowledge. This is because what is certainly true for one person may be certainly false for another. To me, this takes away from the intuitive objectivity of knowledge. If something is certainly true, it must be true for all observers.

Uncertain Knowledge

(Championed by Evidentialism)
Knowledge is that which we know to be true with varying degrees of certainty. No knowledge is ever 100% certain (unless one is omniscient.) In this view, knowledge exists in a spectrum of certainty rather than as an absolute. For example, we may know that things that are almost certainly false (a man flying without the aid of technology), things that are unlikely to be true (me winning the lottery), things that could be true or false (even number of grass blades in my yard), things that are likely to be true (me waking up tomorrow morning), and things that are almost certainly true (Einstein's general relativity).
Like Rand's model, we use the context of our observations and existing knowledge to reach conclusions about new observations. However, because of man's limited knowledge, everything we know is regarded with some degree of uncertainty... however small.

If you haven't already guessed, I favor this definition of knowledge. It is the one I will be using throughout the remainder of my discussion of epistemology... Unless you can convince me a different definition would be more useful and easily communicated?