A weight forward floating line to match the line weight imprinted on the rod (some rods it's on the butt cap) is a good all around line. Scientific Angler and Cortland are both good line manufacturers that offer lines at several price points. As with anything, more cash will get you better quality, although the lowest price lines from either company are still acceptable.
While some prefer a double taper (DT) line because the fact you can reverse the line when one end wears out, the casting advantages of a weight forward (WF) line outweigh (no pun intended) the economy of a DT line. Quality fly lines wear extremely well, and generally do not have to be replaced very often.