4 years Navy as Hospital Corpsman. It all depends on what command you are attached to, and your whether your deployed aboard a ship or stuck on shore duty. They say the further you are from Washington D.C. the more relaxed the commands are. I was lucky enough to get in FMSS. Had a lot of good times... Can be a great way to retire if your down for 20 years.
If you are at sea, don't expect every port call to be fun. Chances are you'll just be on duty/watch. Also a lot of places we make frequent port calls to have restrictions on where we can go. I can confirm Navy has awesome food. I believe they are reducing active billets and gaining rank is somewhat harder compared to other branches. Its not just time in rank/rate that gets you promoted.