I'd have to give it the trio, in this case. I'd have to say that Sadow and Nadd would topple Kressh without too much trouble, and then assist Simus with teh Ragnos. However powerful Ragnos may be, I'm not sure that he can handle his protegé's superior, the former Dark Lord and master magician of his time, and the Dark Jedi who may have slain Sadow.
Ragnos was not leagues above Simus. If he was, they wouldn't have had a titanic battle and it would have just been plain ownage. Sadow and Nadd would clearly be able to bring Kressh down without too much trouble, and then help Simus with Ragnos. I agree with Faunus here, and don't think tha there will be any casualties on the trio's side. Simus maybe, but I see the trio definitely winning this.