Take a look at these numbers and tell me who seems like the better prospect:
Player A - 463 AB/ 18 HR/ 67 RBI/ .288 BA/ .348 OBP/ .814 OPS
Player B - 264 AB/ 18 HR/ 55 RBI/ .295 BA/ .390 OBP/ 1.002 OPS
Player A is two years younger than Player B but you cannot tell me that his numbers are better than Player B's. Both players are about the same size and both players play the same position - catcher. Player A is highly touted prospect Jesus Montero formerly of the Yankees and Player B is Ryan Lavarnway of the Red Sox.
What made me think of checking the numbers on this comparison was this Gordon Edes piece about Lavarnway.
EDIT: MLB.com has a list of the Top 10 Catching Prospects - Montero is listed #1 and Lavarnway is listed #8