The signal loss in a RG59 75 ohm coaxial cable should be of no concern unless you are running over a couple hundred feet. In that case use RG 6.
RG-59. Not used much any more.
By fios, this would be the Verizon fiber-optic service? And, the cable in question is from the set top box to a monitor? Assuming that the answer is yes to both, then a video cable from the set top box should be one with a characteristic impedance of 75ohms. RG58 is a 50ohm cable, so avoid that one. For most short runs of a few feet, then RG6 or almost any other 75ohm co-ax will do the job. For long runs, in excess of 50 feet or so, then the quality of cable can become important to the signal quality received at the television, so a bit more research might be worthwhile. However, there is rarely a "right" or a "wrong" cable to be using as long as it is a 75ohm co-ax.