I have to say Danny Spitz,
I always thought he was the finest lead player of 'the Big Four' - his leads were melodic, thrilling, and the saving graces of an unfortunate album like "Euphoria".
Euphoria is good, but nowhere near as sterling as the albums that preceded and followed, but Spitz' leads are glorious on it
He just had an innate sense of melody and pacing, something Rob is missing in my opinion. I notice it everytime Rob plays a solo in an older track , his solos are competent but he is missing Danny's fluid playing and phrasing.