I use Carbonite currently but both mods are excellent in what they do.
Carbonite has some things that bug the crap out of me. QuestHelper does some things that annoy me but both addons I think are excellent choices depending on what you're looking for in a Questing Mod.
Then again Tourguide is fantastic too.
My reasoning behind my switch was I was having serious issues with routing in cartographer and I use routes
a lot. I heard about Carbonites routing feature and while it's a little flaky works well enough for my strip mining / deflowering of my chosen zones.
