It kinda depends on your preference and what exactly you're doing.
WED is great and easy to work with initially. Quick to make up your forms and shapes. And Oil based clay, like chavant NSP soft or med will be harder to work with initially getting your forms and shapes but you can get more detail and cleaner lines with less work at the end.
Basically one is easier at the beginning and the other is easier at the end. I've almost solely used oil based clays and just started trying out WED and loving it. It's probably a good choice, especially since it sounds like this is your first time doing something like this.
Here's some practice work I've done in WED. Not the greatest of shots but it can give you an idea.
https://www.facebook.com/photo.php?fbid=388619784557544&set=pb.273091412777049.-2207520000.1360113614&type=3&theater
FYI, this pales in comparison do what some people can do with WED.