The minor league leaderboards can always be a bit dicey to look at. While it's a little too early to definitively view the current sample size as large enough, there are still interesting things to note which may be able to help you keep a step ahead of the other owners in your league. With that in mind, let's look at the leaders at each level in the minors in strikeout minus walk rate (K-BB%).
Low-A Leader: Mitch Keller, RHP, Pirates - 36% (Pre-Season Rank: Not Ranked)
Keller was a second round pick by the Pirates back in 2014, and is now in his first full-season assignment after throwing a total of 43 innings in his first two seasons. He's made four starts for Low-A West Virginia, and already has two 10 strikeout games. Interestingly, he had pitch counts of 68 and 71 in those games, both of which had five shutout innings. He wasn't on our top 10 Pirates list this past offseason, but he's definitely a name to look into in deeper formats.
Amazingly, there's nothing new to add here. Urias is a 19 year old in the Pacific Coast League, has a 23:3 K/BB ratio over 18 innings pitched, and realistically could be a mid-rotation starting pitcher before the end of the season. He's a generational prospect given how fast he has moved and his age, and I can't wait to see him in Los Angeles.
High-A Leader: Andrew Suarez, LHP, Giants - 29.4% (Pre-Season Rank: Not Ranked)
Suarez was the Giants' second round pick last year, and the reports on him from the offseason point to a pitcher who has an advanced feel for pitching, even though his raw stuff isn't considered dominant. The best case scenario is likely a pitcher who can be a solid option in most formats, but one that isn't necessarily likely to help carry a staff.
AA Leader: Edwin Diaz, RHP, Mariners - 27% (Pre-Season Rank: #2 SEA)
Diaz returned to AA this season after making 20 starts there in 2015, with the expectation to work on his control and specifically limit his walks. So far through five starts, Diaz has five walks through 27 innings pitched, and has added 35 strikeouts as well. His last start was on Saturday, and was his first where he failed to notch at least seven strikeouts. It appears there are going to be some ups and downs, but the strikeout potential coupled with a favorable home park in the majors make him a candidate for the top 100 by the end of the season.