For me, I like milestone xp if only because without it the only incentive for the players is to solve all problems via combat. I want to run a game where diplomacy or creative thinking can be just as rewarding.
Milestone XP and railroad adventure paths are both the spawn of Hextor. I fart in their general direction. I will give out Quest XP depending on what it is. But in my upcoming S&W game you bet we will be tracking each rat slain and gold piece pilfered.
I think you are mixing two issues together: xp award and railroading. What is your true concern.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.