Making the decisions on my own fantasy keepers has long been a source of frustration and confusion for me. As a result, this year I needed to figure out a way to take my own bias out of these decisions and give myself a basic answer about what a player's value is. And, thus, I created my fantasy baseball keeper formula. It accounts for four things: overall ADP, age, position scarcity and expert rankings. While I think there is a lot more that goes into a player's value than those things, these are the things that should weigh heavily on your decision because they deal most closely with a player's perceived value to the rest of your league.
If you're keeping 5 players, you're essentially taking players for the first five rounds of your draft. So, think of each of those players as picks within that region and value them accordingly. If you have a player that you love for next season but he's going in the 10th round in most drafts, don't waste a keeper spot on him as you can likely grab him in the first few rounds of your draft anyway which will be closer to what his public value is. Succeeding in your drafts is very closely tied to knowing what the market value is for players; the process of choosing your keepers isn't any different.
Here is a quick cheatsheet to judge a player's perceived keeper value for 2011 for a 12-team, 4 keeper league. This is not what I'm touting as a player's true value for 2011 but it gives you an idea of how the rest of your league might perceive the relative keeper strength of each player to give you a better idea of who you might want to let back into the draft and who you want to keep.