Truthfully, I wouldn't worry about your location too much. Personally, we prefer marsh views. We have had pool view during the off season and it was great, but it's too noisy for us during the summer; you might like it though, because you can see your kids at the pool right from your porch!
When we've had "interior" views, it's like being in a small neighborhood, watching everyone going to to and from the pool, etc.
IMHO, there are no bad locations and since the resort is small, nothing is TOO far from any of the amenities.
As far as first or second floor, well, that's personal preference. One of the biggest drawbacks of the HH resort is that the villas do not have very good sound insulation. If you're on the first floor and there is a family with a lot of kids above you, you will hear footsteps. As long as you don't get the group with toddlers who run from room to room at 6 am, it's not too bad, but you never know! (And if you think your kids will be running around a lot, you might prefer the first floor out of consideration for those who would be below you.

) Even the first floor has 1 short flight of stairs (maybe 8-10?) to get to the room; the second floor has 3 of those flights. We usually take our chances on the first floor because when we move in to our villa, we really MOVE IN and it's just easier to not have the extra stairs.
I can truly say that I have never had a bad location at the resort in probably at least 30 visits there over the years -- some that I've prefered over others, maybe, but nothing that I've been unhappy with. You'll enjoy the atmosphere so much, you won't care where your room is, as long as you're in Hilton Head!!!
