If you connect to city water then the 5/8's is my choice. I like a good hard shower and if you restrict the size you restrict the flow. Your pressure gauge should not be higher than 45 pounds so go with the larger hose. If you have a hard time coiling a hose I really feel for you if it is freezing and you have to coil your power cord. lol.
By the by there is only one way to coil the hose do not fight it. As for a cord, any cord, if you give it a half twist when coiling it will be a lot easier. I have coiled thousands of cords in construction for 40 years.