Mariners starting pitcher prospects Danny Hultzen and Taijuan Walker are both off to stellar starts this season -- opening up the possibility their major-league debuts might not be far off. But if you can afford only one bench spot in a seasonal format, then your choice has to be Hultzen, who is 3-1 with a 2.78 ERA and .198 opponents' batting average through four starts in the hitter-friendly Pacific Coast League.
The most obvious sign is Hultzen is at Triple-A and Walker is at Double-A, so unless the Mariners absolutely see competition level not being a factor, then I don't see Walker getting the call before Hultzen, who made 12 starts last season at Triple-A.
That's another encouraging sign. Hultzen struggled last season (5.92 ERA) for Tacoma, but he's a different pitcher this year. Aside from a poor ERA, Hultzen walked 43 batters in 48 2/3 innings last season for Tacoma. This season, he has walked only six batters in 22 2/3 innings. While Walker has a 1.64 ERA and hasn't allowed an earned run in three straight starts (17 innings), he's walked 14 batters in 22 innings, so he clearly needs to work on some command issues.
Unless the Mariners are trying to save an arbitration year on Hultzen by delaying his MLB debut, then he should be first in line when the Mariners need a starter. Perhaps the biggest road block in Hultzen's way is Jeremy Bonderman, who is improving at Triple-A. But if you are looking for a potential impact arm down the road and can afford to be patient, then consider adding Hultzen to your bench.