US dollars are preferred as they are worth more than the Florin by around .50 depending on the exchange rate. So, if you decide to tip someone but tip them 1 Florin instead of 1 American dollar they are getting less, if that makes any sense. I wouldn't want to stand around anywhere to do the conversion, either.
As far as what beach to stay on I would rate Eagle Beach on the top of my list. It is one of the nicest beaches on the island and it is in the middle of the island on the resort side. So if you wanted to go downtown it isn't a far drive to the South, and the marketplace/high rise area isn't a far drive to the North.
Hope that helps!