When evaluating the future value of players I like to use the "ceiling" and "floor" concepts that scouts use, but I also mix in a measure of "probable" result.
It is possible that Player A has both a higher ceiling and floor than Player B, but their most probable or likely results might actually be a little lower than Player B. Maybe Player B is more consistent. Maybe they don't have any threat of injury.
So, for example, let's look at Nelson Cruz and Adam Jones. The ceiling for Cruz is something like .315 with 39 HR, 130 RBI, and 20 SB. However, that would be a full season and he has never played a full season. His floor might be something like .265 with 24 HR, 76 RBI, and 5 SB.
Probably, though, he'll do something like .272 with 25 HR, 88 RBI, and 7 SB.
Let's have a look at Adam Jones. Ceiling: .300 with 32 HR, 110 RBI, 14 SB. His floor? Maybe .262 with 18 HR, 70 RBI, and 6 SB. So, his ceiling is lower and his floor is lower.
But what is most likely with Dr. Jones? I don't know, it is very subjective, but I gotta think something like .280 with 26 HR, 95 RBI, and 12 SB.
Usually when you evaluate players one will have the higher ceiling and the other will have the higher floor. You are gambling upside possibility versus the less risky reliable results option.
Sometimes one player will have the higher ceiling and the higher floor. But, that doesn't mean you automatically pick that guy. Look at the probable outcomes before making your choice.