Omen of whittling

I want to try reroll something on the suffix on my Crossbow but I dont get how the Omen of whittling works, I now know its not the lowest tier that will be removed. Ofcourse I want to keep the attackspeed, so its either life or mana I want to remove. Can someone help me with what of these stats are the lowest-

Expert bombard crossbow

151% increased physical damage - T6
Adds 29 to 50 physical damage - T8
Adds 52 to 79 fire damage - T8
17% increased attack speed - T5
grants 5 life per enemy hit - T4
gain 4 mana per enemy killed - T2


(And PLEASE only reply if you 100% know this, else it might get ruined)



Thanks

Enable the omen and it shows you which mod is gonna get changed

Oh, that I didnt know. THanks for the help.