Each rating is different. ET's and ELT's tend to work the least and get paid the most bonuses with highest multiples. They are the ones to least stay in the Navy. Advancements are faster with ET's because senior ET's leave the Navy for the (easy) $100k jobs.
ELT's on the other hand, you have to be an MM to be an ELT. If you get MM but don't like being a mechanic, i highly recommend you go ELT. However, you'll be doing the same thing day in and day out.... Sample after sample...
EM's life just suck. If you're an EM, tough it out and work on your EWS quals. Your advancement as EM's suck. Their bonus are the lowest. Their multiples are the lowest. They work the longest hours. I have not seen a single EM leave the boat earlier than 1600. They regularly leave around 1700-2000. All I can say is, if you get EM, keep your head up and work on your EWS quals.
MM's are like EM's but with less crappiness while working with machines.