Goblin Engineering FTW.  Explosives are extremely useful, especially the stunning effect, and Goblin Sapper charges are a great surprise if you are gonna die in PVP anyway.  Goblin Jumper Cables can be made and used by both Goblin and Gnome engineers as can the Gnomish Cloaking device (course rogues dont need that hehe).  Gnomish engineers are great, especially the trinkets (Poultriezer, mind control helmet etc)  Both are exceptionally good specializations, all depends on what you will use them for.  PVP Rogues with Goblin Engineers are DEADLY.