I have the same question, so I'll be following this threat :)
If you look at various profiles on Realmplayers, you will see that Omokk's Girth Restrainer is far more popular than Voone's Vice Grips.
I think this is due two things. The belt is plate which makes it an automatic choice if you dont pay attention. The belt is also BiS in some way (Brigam Girdle could be better) so if you plan to get high end gear (Edgemaster's, Devilsaur or the PvP gloves), then belt might be better.
HOWEVER, If you dont plan to get the BoE items, the hit from Voone's Vice Grips will make a huge difference.
For example if you compare Voone's Vice Grips + Valor Belt vs Omokk's Girth Restrainer + Valor Gloves, the choice seems quite obvious?
I am dinging 60 soon and Im really considering to take the Grips because of the huge boost it will be for someone without much hit. However, I am worrying that I might regret it later.
(I believe the AB belt isnt out yet, right? Otherwise that makes the choice obvious...)