General

get legendary ability first for ur main, no matter how much honor exp or nx u waste, then like people said get +1 attack speed, buff duration, %boss, %crit or %drop rate, those are the best abilities u can get.

I think attack speed will benefit you the most. Most dps=more damage

If it's for your Xenon, I'd personally go for Buff Duration

@dulcet: "Boss damage/crit/buff duration/as +1 or drop rate"

This^
I'd 100% go for +1 att speed for your first line unless you can already cap attack speed ((2) without mpe pot, (0) with mpe pot).
Good luck!

that only gives a flat 30 all stat, it is not affected by any %all you have.
Boss damage/crit/buff duration/as +1 or drop rate