I was a junior staff instructor at Charleston Prototype (ELT obviously). Go for all the decision making you want, but the guys in boot camp are going to assign you your rating, and only partially listen to your request (unless you get a rate guaranteed in your contract). At first I was disappointed I didn't get ET because I liked the idea of a sit-down job that worked with electronics and digital circuits. Well thats what I thought all through Power School. Things changed in prototype however, and I suddenly found my place as a Machinists Mate. Its not at all like being a plumber (maybe a little of the maintenance is, but VERY little) but nothing can replace the sheer visceral thrill of spinning up the turbines during warmup (propulsion turbines) standing right between the beasts, and FEELING and HEARING the roar of them fire up at your very command.
I learned to feel sorry for the poor ETs stuck in manuevering because they have to perform flawlessly, since there is an officer watching over their shoulder, and when the higher ranks come down and NRRO (Navy's version of NRC) they always want to see some nifty drills, the central focus of which is usually something to do with the ETs.
Not saying I was prone to making mistakes as an MM, but it is more forgiving if you do. Its pretty tough to SCRAM the plant as an MM, it's possible but you pretty much must intentionally do it.
I'd have to say ETs have the easiest job but requires the most prepping, study, and expertise to wisely respond to any number of scenarios in a split second, knowing all the switches and controls and readings in front of them like they know their own name. Another drawback is EVERYBODY knows your job so when you do make a small mistake everybody knows about it and will jump all over you.
On the flip side, if you are a smart and congenial as an MM you can get picked up as an ELT like I did. I think ELT has the greatest job in the NAVY (and if I somehow get dropped from STA-21 I won't be that sad because I still get to go out to the fleet to be an ELT, oh no don't do that!). The knowledge level and expertise of an ELT rival that of the ETs, except our knowledge is pretty exclusive. Every rating gets cross-rate knowledge (ie mechanics learn basics of all electrical systems) but nobody really gets farther than basic understanding of ELT material. This leads to us having to explain things much of the time, and just as with the ET, being an ELT leads to lots of face to face time with the captain, XO, NRRO, and lots of officers. A very political job that concerns everybody to the top of the chain of command and many concerned civilians.
I think it is a draw between MM and EM, they both do tons of maintenance, and EO (Electric Plant Operator) can be a crap deal in some instances (watch how fast a careless EO can SCRAM the plant). But if you want a shot at ELT you gotta be a mechanic. In my experience at prototype (almost 2 years of instructor duty before shipping off to STA-21) as an ELT instructor I saw about 2 ELTs out of a crew of say 12 mechanics get picked up to be an ELT, usually based on how much the Mechanic Chief likes you (and your MDiv LPO). If no staff likes you forget about being an ELT, even if you are the smartest nuke this side of the pacific