Top 5 Minor league system (I am only considering players who have not made appearances in the majors):
1)
Offence leadby Sano and Myers, arguably the the top two hitters in minor league baseball. Bonifaco and Bradley has also broke out, and system can become better when Rendon gets healthy. Pitching is lead by Miller / Lee / Banuelos and the recovery Matzek. Big names here but none of them have started extremely well. Best system in the league by far and could get better with the upcoming draft and trade deadline.
Sleeper: Rougned Odor - 18 y/o holding his own in A ball.
2)
Those BA superscriptions are paying off. Could have been in the running for no. 1 if Middlebrooks didn't get called up. Arenado is going to be a monster at Coors. Schoop / Liriano / Cron are also very interested fantasy wise. Pitching is probably the best in the game with Walker (nice trade) / Harvey / Peacock / Pomeranz / Rosenthal / Matias. The ammunition is definitely there for Roy to make a big move for the playoff run.
Sleeper: Trevor Rosenthal: probably ends up in the top 100 prospect list by the end of the year...might even push for top 50.
3)
Credit goes out to Ben for having such good system well making virtually no moves. Offensce is lead by Machado but there are so many other good players like Marisnick / Sanchez / Norris / Hedges/ Siwart / Castellanos / Choice / Gyorko / Nimmo. Unlike most teams, Ben's top prospects are in EDR which is arguably make these players more valuable as they are not taking up major league roster spots. With another 7 or so picks coming up in the first round of this year draft, the system will get even stronger.
Sleeper: Jesee Biddle - bit of a forgotten man as he does not get as much hype as others. The pedigrees are there and he has cut down on the walks and increased his strike outs this year.
4)
Would have been ranked higher if Harper is still in the minors. Profar / Simmons should keep the MI position stable for a long time. After struggling last year, Sale has hit a lot better this year and with more patience while moving up a level. Not too many interesting name on the pitching side besides Bauer and Gilmartin but both of them can help starting next year.
Sleeper: Ryan Brett: he is hitting very well this year and I have heard some good things.
5)
I am probably biased but I like my system. On the hitting side, Goodwin / Williams have tremendous upside and have performed very well this year. In season pick ups of Hanson and Lake have also done well. There are a lot of interesting names that could break out here. The pitching is lead by the big 4 of Hultzen / Skaggs / Nicolino / Paxton. Another name worth noting is Brett Mooneyham who will probably get drafted in the supplementary round of the (real) MLB draft.
Sleeper: Nicky Delmonico - first round talent but got pushed down to the 4th round due to bonus demand. Has an OPS close to .800 in A ball while playing 2B.
Just missed the top 5: