Guitar Pro.
I've got 5 on my laptop, the guitarist in my band gave me his copy so he can write guitar, email me the track and I add drums, and the best thing is it all goes onto one score.
Works for us... you can add lyrics onto the score to, so you can figure out how a song can be constructed easily.
Only thing you can't do easily is writing in the \\ repeat phrases and note on ppp, pp, p, mp, mf, f, ff, sff.