I woud do two rectangle but make sure they have a streamlined metal frame. Something like this

Metal Frame Rectangle Mirror 24" Black · More Info

Metal Frame Rectangle Mirror 24 Inch Silver · More Info

You need to measure your space i posted for style reference only to show what i meant by thin metal frame . This type of mirror comes in multiple sizes so it just depends on what size you’ll need.

I have this mirror/medicine cabinet installed in my bathroom. It looks great and serves as convenient storage. It is mirrored inside which is surprisingly useful. I see you already have lights installed over the mirror. I really like my lights on either side. The illumination is so much better.

Kohler medicine cabinet at Lowe's

One large wall-to-wall mirror to maximize what is a very tight space. Even better, wall-to-wall and from the top of the vanity to the ceiling with cutouts for the fixtures.

I'd say one large mirror to maixmize the space and to avoid the space looking too crowded.

One- agree it would expand the space. Also, if you step a bit over to the middle while grooming, you're still in the mirror. :)

I like the two elongated rectangular mirrors. Makes the room look taller and more interesting. The one piece mirror or all around mirror appears a bit dated. Just my opinion.