Now if I was voting based on my first rides on both of these coasters in 2012 there would only have been one winner; Oz'Iris. Back then Wodan was relatively tame whereas Oz'Iris was B&M back to their best.
Fast forward to today and I still have not been back to Asterix. However Wodan has grown so much since it opened, what with running different wheels and generally bedding it, it seems to get better year and year.
So Wodan easily takes this for me.