Dont have any experience with spax coilovers but I did have a set of their fixed and didnt think much of them. saying that though I have'nt read much bad about their coilovers
With the Wietecs they come in 3 types, GTN and GT I'm not sure what the difference is but I know the GTN is cheaper, there damping is set at around 30%. They also have a TX kit which has adjustable damping