Pros
Pay - unless you have multiple spouses in Olongopo or Pattaya, you will not live pay check to pay check. You will, however, question how much you sold your soul for after going into Djibouti for the umpteenth time in the middle of summer. Travel - you'll be the envy of all your friends on the Book of Face showing off all the places you go: Singapore, Dubai, Greece, Sicily, Japan, Australia. And, unlike commercial mariners, you'll even have time to explore these places. That said, most of your colleagues won't travel further than the NEX or the closest working ladies bar. Mission - you really do impact the mission of the US Military and the Navy in particular. It's much more rewarding supplying the nation's sailors at sea than moving containers of Chinese-made flip-flops for Wal-Mart. It's easy - compared to the responsibilities required for commercial mariners, "it's good enough for government work" is the vibe here; which leads me to the cons at working with MSC:
Cons
Incompetence - after you completed your first year probationary period, it takes an act from god to get fired. I have sailed with third mates who couldn't plot a position on a chart and A/B's who couldn't tie a bowline knot. Length of tours - it's a minimum 4 month tour at sea and one month off. There are a LOT of broken marriages here. Culture - MSC combines the worst elements of the government and private sectors. You have the bureaucracy and inefficiency of the US Navy combined with Corporate America managerial B.S. Shore-side staff - honestly, they would rather play CandyCrush on their phones all day than respond to your email.