People saying Pioneer? Are you insane!? The total value you get out of Pioneer's EXP boost if you do it first is most likely going to completely outweigh the utility you get out of any other specialization over the course of your entire Halo 4 career.
What, you think that just because something doesn't work once you're max level that it's useless? Pardon me if I say poppycock. POPPYCOCK!
Pioneer will save you a ton of grief, and just how long were you expecting to play Halo 4 anyway, such that you'd feel that a fast-track to higher level is somehow the "worst" specialization you can have?
A specialization that is only useful until max level is still far more useful than a specialization that is useless the entire way to max level and continues to be useless beyond that. (I'm talking about Stalker by the way.)
Is there something about the way I type that makes it sound angry? Maybe it's just something about the way you read.