Pros
I can only speak for Engineering: A superb choice for people with no obligations to silly land-lubbery (home, family, etc.). Very high upward mobility.... not unheard of to go from Third Engineer to First Engineer in only four years. You do the time, you eventually get promoted through their internal process. Many different large platforms (diesel, steam and gas turbine ships mostly designed for delivery of fuel and food at sea to Navy ships, though some other have special purposes. Federal job and perfect for the job security including those who have BumbleBee Tuna for brains. Most people here are competent. Provides ample learning experiences. Tons of overtime. With OT included, gross income for 3A/E ranges from $100,000 to $150,00 depending on how much vacation time taken and size/type of ship assigned to. 2A/E can get to $185,000+. Advice to young Engineering Officers: Do a few years, save that money then get out and get a life.
Cons
If you are overly jealous of union-affiliated, oil tanker or offshore drill rig mariners who spend half their year on vacation, MSC is not for you. Four months is a typical tour, though as an Engineer you are often relieved a month late, so in essence five month tours. After one month vacation you get called in again. Do not expect to have much of a life beyond MSC. New entry-level engineers flee from this organization regularly due to lack of vacation. Drop-out rate for maritime school grads is very high within first few years.