If you know how to do a fishless cycle, it's definitely preferable to do it that way. It's not hard, it's not expensive, and it does give you a better understanding of how your fish are able to live in a tank.
It will also give your fish a longer and healthier life. Ammonia has several effects on the fish's gills and can decrease its oxygen uptake ability. Nitrites destroy the hemoglobin, making the bloodstream less able to carry oxygen.