I don't know why you peeps ask this question on Graalians. A majority of people here don't even like Era. You would have much better luck and answers over at Era-Go.
With that being said, set your MPX gun stats to where your most comfortable. Do you prefer more spread, freeze, ROF? I barely did MPX but I found when I set my gun to how I felt, I could win more battles. But yeah, go on Era Go and speak to the people who actually do MPX there to get more insight.