Re: newbe to the salt
You should be fine with either a floater or an intermediate in either situation.
The Intermediate sinks slow enough that it will be fine on the flats too unless they're really shallow. If you had a fast sinking line that might be a useful for deep water close to shore like channel edges etc. but would probably not be as useful in gradually sloping sand beaches and wadeable flats.
An intermediate will get you below the surface chop, but is not as easy to mend (if you have a sweeping current to the left or right), and it's more difficult to lift line out of the water for casts (either slack line at your feet, or lifting line out of your rod tip to reposition the fly) because of the added resistance you'll get from trying to pull it through several inches of water. It will help to get you fly a bit deeper, I generally use a short leader of straight 20lb mono (3-4") with an intermediate.
A floater will allow you to mend easier but will be affected by wave action.
So "six of one, half dozen of the other"-- pick the one you can cast the best and go at it.