I always leveled up lockpicking. It comes in handy!
Junkboxes are mostly junk, you can use them to get materials for poisons and some other random gear but to me it was never worth the effort. (That's just my opinion though, other rogues might feel differently) They can be helpful to level lock picking. Especially on this server due to some dead spots with poor footlocker respawns. You can follow this guide from wowikki (
http://wowwiki.wikia.com/wiki/Junkbox) to see what level of mobs you can pickpocket junkboxes from.
My memory is pretty hazy, but I think you can do this to level
- At 125 you should be high enough for the Murloc camps in the Wetlands. Along the west coast just north of the Alliance town you'll find a few footlockers on a fairly short spawn timer.
- At 175 move to Desolace. IIRC there are 7 lockboxes on a 3 or so minute timer at the bottom of the sea where the Naga are. Around 33,17 (near the underwater Gazebo). You can use those to level up until you're high enough for Searing Gorge. Make sure to bring an underwater breathing elixir or you'll have to swim up all the time between lockboxes (Credit goes to Poepinjehoofd!!)
- At 225 (again, maybe lower, this is just what I did) I went to the Slag Pit in Searing gorge. Few boxes there on an okay timer. But I want to say I mostly pick pocket the mobs.
- At 250 go to Tyr's hand in Eastern Plauge lands. Scarlet Junkboxes are there and most of them have a good respawn rate. They will take you all the way to 300 fairly quickly.
- At 300, Zangarmarsh, I can't think of the name of the place :( but its sort of south east from the horde camp. There is a camp with wicker chests you can pick all the way to 350 (I stayed here because the respawn rate at the next location most people recommend was awful).
Hope that helps!