Well I've finally decided on going for an empy on my DRK, and was wondering which one would be the better choice, for example what one has the better range on WS damage, which one would you chose, and so on.
I have both. Make caladbolg, hands down. While redemption is nice for the high-defense voidwalkers, I find myself using calad 9 times out of 10. If you don't mind using red curry buns and/or making situational "high attack" sets, you'll make the window of redemption even smaller.
To put it in perspective: I use my redemption about twice as often as I use my twilight scythe. I do happen to use redemption a lot of times with a 5-hit build to chain darknesses with my set-mates twashtar but that is also situational (and more fun).