Spin for PvE, Eviscerate for PvP 
Always use spin PvE side because its easier to hit multiple targets since its a PBAoE and not a crappy melee cone. PvP AoEs are useless anyway because of loldamage.
In PvE your much more likely to find yourself against multiple foes, particularly ones who block you so you cant line them up for eviscerate to hit them all. Spin is a million times easier to manage and although it does less damage its not too much different and its more reliable to use. 2s extra recharge is nothing for a lot more mobs hit.
This goes for both claws and widow.
Hmmm... good points there.
I prefer Spin due to the higher target cap, and the animation *feels* faster/smoother even if it isn't really.
However, I took both and would advocate (at least for PvE) that others do the same.
They are both good powers indeed, but i do leave out eviscerate because it actually lowers my DPS rather than raises it due to the attack time and amount of targets it hits. All the other claws attacks animate in under a second, so make for decent dps because of stacking them very quickly.
Eviscerate slows this whole process down, as does spin but spin hits more targets so keeps dps the same or more overall where as eviscerate commonly just hits two or three targets with its long animation time which is why i leave it.
Ive heard people actually complain spin is overpowered on these forums before, I only hear eviscerate is underpowered lol.
Did some testing, think I'm going to stick with spin. Eviscerate is nice, but yeah it seems to animate forever (even though it and spin have the same activation times), and I noticed today that spin allows me to do something eviscerate cannot: I can still hit a mob that has blinded/placated me with it. Glad I do all my stress testing in the GV fab heh.
Ok thanks again for the feedback guys!
Personally I hate Spin and even if it hits multiple targets the damage isn't really all that great. I have both on my Night Widow, but I took Spin much later in the build. Eviscerate is a power I love because it does great damage and it can hit multiple enemies. Having gained a lot experience with that power from my Spines/Willpower Scrapper, it was a no brainer when I first had the choice between the two.
"People love to talk, but hate to listen." Alice Duer Miller, American Author (1874-1942)
i didnt go with the night widow path, but on my claws brute i took both eviscerate and the equivalent of spin because they both can hit more than 1 target
IMO eviscerate is higher dmg while spin is much lower dmg, i would get both because spin can hit more targets and cant hit foes you cant see, while eviscerate is a stronger attack that if you line up right can hit a bunch of baddies as well (i personally also think the animation is pretty neat too)
Which do you guys prefer and why? I've always used spin on my NW and have no experience with eviscerate, on paper eviscerate hits way harder and I can see it even being part of a single attack chain (it hits harder than lunge does, and it's also an AE that will affect up to 5 targets). It has the same cast time as spin and less endurance per activation as well.
Part of the reason I want to try it out as well is it is one of a NW's signature attacks: my fort has spin and FU just like my NW does, the only physical claw attack that differs between my 2 builds is slash. The advantage of spin is you can just let it rip and hit everything around you (and it has twice the target cap as eviscerate), but I have no problem stepping back a few feet to line mobs up in a cone and I rarely have more than 5 mobs on me at once so I don't see the advantage of spin over eviscerate for my playstyle.
Just curious who using it and what their experience is with it is all. Thanks guys.