What do you want to do job wise?
For instance Army, Navy, and Air Force Engineers do similar work... but we do it in different ways. SEA BEEs (Navy engineers) do a lot of work for the Army and Air Force, and are usually "in the shi*" Air Force engineers deploy in 3 categories... we deploy for ourselves in a Base Maint. role, as RED HORSE (similar to SEA BEEs) with a broad construction responsibility, and in support of the Army. Army engineers are in short supply doing mostly IED removal/road repair DEEP in the "shi*".
While all of those experiances will net you a decent civilian job, the Air Force and Navy jobs will give you a broader skill set. The Marines have engineers as well, but you hardly see them.
If you want something that translates well to the civilian life, go Navy or Air Force. If you want to make a difference from up front, join the Army or Marines.
As far as Mechanical jobs go I'd lean towards Navy or Army (both directly deal with high dollar mechanic jobs on the "outside")
I think the Navy has the best Medical program followed by the Air Force and Army (Sorry Marines, not forgetting you guys, it's just most Marine meds are trained towards sustaining a patient where the other services lean towards a hospital environment)
Electronics, all 4 services have outstanding areas and all those areas become HIGH dollar civy jobs
Cooks... This ones debatable, I think Air Force cooks have the best training, but Navy and Army cooks push forward the best food.
Other jobs... I'm not familiar with.
I'm an Air Force Engineer and have worked with all the services, from that exposure the Air Force and Navy are close together... What we do as one career field translated to the Army is multiple fields... for example...
Say I Drive a Stang, a Ferrari, a Porsche, and a Honda...
The Army would have 4 different people to do that
The Navy would have 2 overlapping jobs doing that
The Marines would have some one who CAN do all that, but is only trained to drive the Honda (because unfortunately they get the crappiest equipment)