It's hard to say because it truly does depend on the individual and all of the many habits and patterns that make them bring whatever it is they bring to a woman (or man).
Generally speaking, it's better to be a relationship guy because well... in all truthfulness... ONS guys are basically just another notch on someone's dildo and nothing more. That may sound appealing if they're afraid or not interested in something more serious but kinda sorta basically being a dildo with a heartbeat will never be as fulfilling and enriching as being someone's partner in life. Pussy will never be able to give what a heart can.
I had "meaningless" sex in the past. ONS were men who were bad. When it was good, I would see the guys again. Why bother go for a new man each time when you can have it good with one. The relationship guy? He take the time to know your body, he brings feelings into the mix. It's heaven.