Pitching is a precious commodity and one of the most difficult to evaluate. If we were in position to do a careful analysis of every pitcher who was called up to the majors this year, we would be best served to wait a few starts. Give the guy some time to acclimate to his new environment or prove he does not belong.
But we don't have that luxury. As soon as a hurler posts any reasonable pitching line, the foragers are out in force. Before we have even a second data point, he is gone. Within a few weeks we'll know whether his lucky owner is a genius or an idiot.
The following pitchers are likely already rostered in deep leagues, but you might better consider them as prime trade bait. In shallow leagues, don't bother with them at all.