I would suggest a good quality water-based polyurethane - satin. Water-based poly coatings have improved a great deal in recent years and they apply much more easily than oil-based finishes. The principal drawback with using the water-based coatings is that you have to put on many coats (most recommend at least three, I typically us five thin coats), and the color is not quite as good as what you obtain with the oil-based coatings.
One piece of advice before you put on a finish to the floor: I am not sure what type of sander you used to refinish the floor. If it was a drum sander, you want to check very carefully for depressions in the wood (it is very difficult to see them without the poly coating, but the poly coating will definitely bring them out!)