I'd have to say that Eddga is by far more useful than Osiris card.. While I can agree that Osiris could be useful in the combination with kaizel but that's about it. Normally you're able to get a heal after you ressurect or go to an inn if you respawn in town.
While Eddga has takes 25% of your hp it does give you perma endure. It can be useful for assassins when they are mobbing like JJJ said. Even though you aren't supposed to get hit, having this card would save you IF you got hit. Otherwise, getting hit once would get you killed 90% of the time. The other 10% would be if you managed to get yourself hidden before dying. Which is rare if you are mobbing the 50% of the map.
Also agree that Eddga is useful for the swordman classes (even though they could just as well use their own endure skill and not lose 25% of their hp) and the priest class.
However, osiris.. In my eyes, that card is ONLY good for kaizel...So my vote goes for osiris as the worst MvP card.