I would choose a vertical rectangle. are you adding a lamp?

You have lots of options. Depends on how the rest of the home is styled.

I was thinking a simple round mirror. havent gotren to styling yet but was thinking a lamp for height

i'd select a 48" diameter mirror. Don't select a mirror that's too small.

Cut kraft paper in different standard sizes (even shapes) and tape to wall to help with your decision as well as its height. Be sure to have a few lamps and accessories (that can be returned) and test until you are happy with the vignette’s balance.

I usually prefer art instaed of mirrors since often a mirror reflects nothing worth seeing twice.. First figure out what will be reflected and IMO art is always more interestling in an entry