Well, the spellthief was weak, and even in what ways it wasn't, it was kind of dependent on fighting arcane casters to really be at full strength. It really should have been a Prestige Class, something to build onto a sold rogue/caster core. Even with its own limited casting and decent sneak attack progression, it just remained behind the curve. It's also one of those classes that brings to mind the musical question: "Could this be a feat chain?"
I don't think the Marshal and Hexblade really got more love, except insofar as they had longevity on their side. The Marshal is slightly weak, but resides in its own niche, much like the Fighter or Barbarian. The Hexblade... as long as you understand what the class was, it could hold its own against most of the core classes. The spellthief fared better than the Swashbuckler, everyone's favorite half-assed fusion of fighter, rogue, and low damage output, and the Samurai, the class for people who like fighters but don't want useful abilities.
The Scout... hardly needed support. It came out of the gate quite strong and versatile, with many fun ways to play it. Since its skirmish ability first appeared in the Highlands Stalker Prestige Class, it had a decent prestige option before it was even born.
The Ninja... slightly weak Rogue. But invisibility is nice, so yeah. It's the Beguiler of Rogues.
