Guitar Pro all the way. Ive been in several bands that will literally write entire songs using that program. You can email the files in seconds, so you can keep altering parts by sending files back and forward over MSN chat etc, then email it out to the whole band. Everyone learns their parts on their own then you can just turn up to the rehearsal and nail it in one!!...in theory
The drums are a big plus since you get a much better sense of a riff's feel when you can experiment with different drum grooves underneath it. PLus you can have many more instrument lines than you can in guitar pro, aswell as beter articulation/dynamics controls.