If yout asking which out of the three to do next, gear the hunter if you have a friend who will be a pocket healer, forget locks since they suck and make the feral if you wanna get insane crits when geared. I think you know which I would chose.
I'm on my 30th engineering re-level, Yet to get synapse. It could be he doesn't want to shell out, Spend the time, Doesn't want to be that feral that's made fun of for 'crutching' on 25k Fero bites, Or prefers to opt for another profession that has a slightly less chance of being nerfed in the future (ie; 500 Engineering requirement on tinkers.).
And really, I'd either work on the hunter, Or the druid. Seeing as how druids are going to be fantastic come MoP, And hunter's are great, Once you get the hang of it. Save the 3900 AP tinker rogues that'll open on you inside your flare, Kill you inside a CS, even with RoS up, All whilst mashing their emote macro(s).