Well if I were going to compare them I'd look at xERA and then the pitchers career trends compared to it and park he is in. xERA shows very strong correlation year to year and adjusts based on changes in skills not changes in things like strand rate and hit rate. It factors in BB's, K's and GB% which are the biggest keys to pitching. What xERA doesn't do is account for pitchers who don't fit the 'typical' mold so you have to look at a players career trends and modify xERA based on those to get a true skill level. Livan has had a 4.04, 4.65, 5.13, 5.55 xERA the last four years a pretty clear downward trend. his BB/9 are going up, K/9 going down and FB% is going up which are all bad things. He has a pretty clear cut trend of beating his xERA mostly because he has above average strand rates and pitched in a park that suppresses his HR's so I'd say something around a 5 ERA is what he pitched like last year. Park adjust that and it looks even worse. Bush has had a 4.23, 4.23, 3.49, 4.18 xERA the past four years which is a pretty steady skillset. He is the opposite of Livan showing a career long pattern of low strand rates and giving up too many HR's. I'd say he pitched something around a 4.55 ERA last year from a skills standpoint. Park adjust that and it looks a little bit better. In this case the most likely culprit is team defense. Livan had the lowest hit rate of his last four years this season and Bush had his highest, which isn't surprising since Arizona was a strong defensive team and the Brewers one of the worst in baseball.