i've used wonderflex for a few cosplay pieces. i just got in some worbla and i'm really looking forward to trying it. it seems a lot more versatile than wonderflex. wf has the mesh that helps its durability but it can also interfere with working with it. i've also had some issues with wonderflex unsticking from itself when using the foam method, with the foam between two wf pieces. that's probably due to my own mistakes though.
worbla seems to be able to be used for a lot more. others mentioned kamui using it, her work with it convinced me to try it. i like that she can use it to directly form the cups for her chest pieces, since thats where almost all my construction issues are. check out lightning cosplay's
facebook page too, she just made these awesome skull pieces by shaping them out of clay first and then using worbla on them.