SSD4 for drums hands down. Not sure about the guitar sims. Depends on genre. Actually, so does the drum software, but the Steven Slate stuff sounds the most 'real' to me.
Cheers . I'm probably gonna go with Superior Drummer 2.0 and just download all of the tones compatible with my LINE 6 UX2 POD for now. I'm gonna get a bass for Christmas aswell. I'm only looking to start doing some solid song writing / demos and so I'm not too fussed about the best of the best gear right now. Superior Drummer and Steven Slate and Addictive Drummer are the ones I've been looking at and they all look amazing to use and sound proffesional / human as anything. The review of Superior 2.0 on youtube blew me away; all of the mixing possibilities and kit setup options!