Dave Navarro for sure.
He's a great guitar player, no mega virtuoso that can play piruriru picksweeping 300 notes per second, but he has the goods and delivers. His guitar work with Jane's Addiction has been great and I live what he did with the Peppers -One Hot Minute is by far their darkest and most interesting album- and Deconstruction was GENIUS (even if that's big part Eric Avery).
Axl wanted Dave in GNR in the beginning of the band. Dave and Slash were THE 2 well known guitar players in LA in the mid-late '80s. In the end, Dave agreed to tour with them later when GNR were STADIUM big, but he just didn't show up because at that time in his life he was too fucked up on heroin.
And well, years later there's Oh My God...