Correcting tooth discolouration is more predictable with a crown.
If the tooth is severely discoloured, more porcelain needs to be layered on top of it to mask it. Generally, this means that ultra-thin veneers are out because there would not be enough material thickness.
It can be very challenging to mask a discoloured tooth and match it to to adjacent natural teeth, so expect a few try-ins or even remakes of the final crown to get the best results.
If the entire root is also discoloured, this may show through the gumline at the end and may not be masked by the crown. This may appear as a grey or dark gum. If the crown is opaque, the lack of light transmission at the gumline (especially if the patient has a low lip line when smiling) may make the gum discolouration significant. A gum graft to increase the amount of soft tissue coverage may be needed to mask the dark root.