Finck. Hes got more of an emotion behind his playing. Fortus can shread like hell, he is more than capable of handling Buckets solos and IMO, they don`t need another guitarist.
They never needed. But Axl thought it was a good idea. And I'm with him... You can always put Fortus to play Bucket's solos, it doesn't matter. But some new songs will need 3 guitars live, I guess. They can handle with 2 guitar players, but it would be way better for them to have another guitarist.
BTW, Finck plays some licks in Maddie solo. Just keep in that way and put someone else (Fortus, new guy) to play the solo while Finck do his amazing guitar work in this song.
Or maybe they could put me playing the solo:
Check it out!