Jackson is 3-6 with a 2.52 ERA and .194 opponents' batting average in 12 starts. He has struck out 77 batters, walked 29 and allowed six home runs in 71 1/3 innings. Unfortunately, he's winless in his last six starts (0-4).

Walker has managed 32 strikeouts through 29 innings, which has him tied with White Sox prospect Erik Johnson and Brewers prospect Jimmy Nelson for the Southern League lead. Walker is 2-2 with a 1.55 ERA and .150 opponents' batting average. He's also issued four walks in four of his five starts and 18 total on the season.

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.

Ranked as baseball's 18th-best prospect by Baseball America and fifth-best prospect by MLB.com this offseason, Walker allowed four earned runs on seven hits and five walks with four strikeouts in seven innings this spring.

Paxton, who also made the top 100 in both prospect lists, allowed six earned runs on six hits and four walks in 3 2/3 innings with just one strikeout this spring. Nunez pitched just two innings, allowing seven runs (four earned).