On (the) one hand ...

on the (one) hand

Does anyone know if it's considered better to say:

on one hand, it's great, but ...
or
on the one hand it's great, but ...

Steve (BE) says:
"I think I would probably say either, but in writing I'd prefer to use the article, for reasons of symmetry"

The OED says:
"on (the) one hand, on the other hand" are used to indicate two contrasted sides of a subject, circumstances, considerations, points of view, etc."