Finding comps for hitters was much easier than for the pitchers. So many pitchers flame out, have good stats due to pitchability or get injured. Pitchers are so hard to quantify, but here is what I came up with.
Manuel Banuelos and Martin Perez were both 18 year olds in the SALLY league this season and both are very good prospects. Perez did pitch a little bit in AA this season but the only other 18 year old I have stats on in the Texas league is Felix Hernandez in 2004. Looking at Perez and Banuelos SALLY stats, the comparables jump out as Matt Cain in 2003, Francisco Liriano in 2002 and fellow prospect Brandon Erbe in 2006. Jose Rojas' 2001 season is similar to Banuelos and but Banuelos had a slightly better K rate.
Madison Bumgarner had an unusual season in AA. He really had no comps as he had the lowest K rate and BB rate of any 19 year old in AA that I have. He also had the lowest WHIP of the group and Matt Cain, Joel Zumaya, Hayden Penn, Yusmeiro Petit and Rodney Nye. Bumgarner's stats in High A were comparable to Jerome Williams in 2000, TJ Nall in 2000 and Edgar Gonzalez in 2002.
Chris Tillman is a little easier to nail down. His comparisons are 2005 Boof Bonser, 1995 Paul Wilson and 2005 Brandon McCarthy. He has more to work with as for Age to league comps.