On camera flash
On camera flash gives the worst result but there are ways of improving it. I highly rate Nikon’s CCS system, I use a pair of SB800’s now quite old but work well.
In auto using a cameras modern TTL flash metering system you generally get reasonable results, but they become easily tricked by large dark or white areas.
You get a bounce card with the SB800’s that helps and a little modifier, you can also buy little soft boxes to fit on the flash to improve things.
I generally use one flash on camera on low power giving some fill, with a second SB800 on a stand to the side providing the main light. In this shot above of Holly above, I think it was a battery powered Quadra on a stand providing the light with a shoot through brolly.