I may be a little bit late on this, as I've missed a solid two weeks of minor league performances, but I thought I should highlight the Sox farmhand at each position who had the best first-half.
1B -- Casey Rogowski | AAA Charlotte | .273/.361/.415 5 HR 19 2B
Rogowski is a doubles hitter who is trapped behind Thome, Konerko, and even Ross Gload. He doesn't figure to be anything more than a back-up at 1B, and more likely a AAAA player. Still, he gets the nod as the best 1B in our system.
2B -- Andy Gonzalez | AAA Charlotte | .301/.398/.414 2 HR 15 2B
A few years ago, Gonzalez was part of a trio of promising SS prospects in the White Sox organization. Gonzo was the least defensive-minded of the group, and thus was moved to 2B. He has shown surprising plate discipline this season, but continues his only-adequate defense, leading the Knights in errors. He could be used as a utility man in the future, though it would be hard to break into the current Sox roster.
3B -- Josh Fields | AAA Charlotte | .328/.410/.563 12 HR 20 2B
Fields has rebounded from a disappointing performance in AA to sit atop the entire International League in OPS. He's still striking out at an alarming rate, but he put himself on the radar as an elite prospect with plus power and plus athleticism.
SS -- Pass
Pedro Lopez carries a .311 OBP in Charlotte, and Robert Valido is in the process of falling off the prospect landscape. No prospects are worthy of mention here.
OF -- Ryan Sweeney | AAA Charlotte | .309/.355/.426 5HR 8 2B
To paraphrase Bull Pain, Sweeney continues to be the type of prospect that looks like he'll be a good hitter, but hasn't quite shown it yet. Sweeney's youth, his ability to make contact, and his high average make him possibly the Sox top position prospect.
OF -- Ricardo Nanita | AA Birmingham | .277/.364/.399 6HR 11 2B
Nanita is often overlooked. He's a bit old for a prospect, but has always demonstrated excellent control of the strikezone. If he continues his development, he's a good bet to be a useful 4th outfielder.
OF -- Inc.
I suspect that this spot would have been filled by Aaron Cunningham, had he stayed healthy. But He's only had about 10 at-bats in the past 2 months. It says quite a lot about the Sox minor league OF depth that I can't put together a list with a single 'prospect' with an OPS above .800.
SP -- Lucas Harrell | High-A Winston-Salem | 7-1, 1.85 ERA
Harrell has come out of nowhere to be considered one of the best starting pitching prospects the Sox have. He's dominated the Carolina League from the very first week of the season, culminating in an impressive May that featured two near-no-hitters and only a handful of balls hit in the air against him. He's slowed down a bit in June, but he should still get a taste of AA before the season is done.
SP -- Tyler Lumsden | AA Birmingham | 8-2, 2.83 ERA
Lumsden did not pitch in any meaningful games at all last season, spending the year in Arizona rehabbing from surgery. He's rebounded with strong showing at AA Birmingham. He's started 16 games this season, and 12 of them could be considered 'lights out.' The other 4, however, are poor enough to more than double his ERA. For example, in his last 10 starts, he allowed a total of 3 earned runs in 8 of them, but allowed 13 earned runs in the other two. If Lumsden can limit the poor outings, he'll become an elite prospect. He already has the 'best stuff' of any White Sox starting pitching prospect.
SP -- Heath Phillips | AAA Charlotte | 10-2 1.76 ERA
Phillips has put himself in a position where he'll probably be dealt at the trade deadline. He leads the IL in wins, and ranks third in ERA. Like Mark Buehrle, you won't hear anyone raving about his stuff, and he features a great pick-off move. Still, he profiles as a back-of-the-rotation guy, and that's not the type of pitcher who the Sox figure to keep around.
It should come as no surprise that the Charlotte Knights dominate this list. They boast the best record in minor league baseball, and just had 6 players named to the International League All-Star team.