Under what types of conditions will it be used? For example...if you are shooting outdoors in bright sunlight, you should consider a more powerful flash. Will it be used in softboxes or other types of light modifiers? Do you want HSS - a feature that will allow outdoor flash with higher than normal shutter sync speeds.
The Godox V860II that Horoscope Fish mentioned is great. Down the road, you can add a Godox trigger if you are looking to use the flash off camera. Both Godox and Yongnuo make good flashes that are less expensive than the Nikon brand flashes.