Third mirror seems to go best with the other pieces.

How about this:

I'd choose #3 also.

#3 - Its gonna be beautiful!

#3. Fourth pick is nice too.

I really like #2! What a lovely bathroom it will be!

i would choose #1 or the one that tibbrix posted... but, they would all look fine... it really comes down to your personal taste!

Although all the mirrors are very nice, I like the rectangular shape of #1 because it mimics the shape of your sink & cabinet doors, and won't fight with the shape of your light fixtures once installed on the wall.

The only thing I don't like about #1 is the antique glass in the frame & the decorations at the miter. I would suggest something a bit more simple like the two mirrors at the bottom from Restoration Hardware.

After seeing the mock up Beverly did, I think I do prefer option 1 or something rectangular.

In agreement that they are all fine choices, but my preference is for the first one. I am not able to explain why, but I prefer that one.

I like #3 because everything else is rectangular and because of the finish. Plus it picks up a little on the ceiling fixture.

Agree with noscoccermom. #3 is an angular mirror, so it will be fine with the square sink, but the corners add some interest. Mostly, though, I think the thickness and those corners make that mirror fit best with the sconces, which will be right next to it.

The sink is not centured over the vanity so the mirrors your looking at won,t be either . Will that bother you? If so mirror that is wider than those shown might be the best choice. If not I like the first one because it reflects the shape of the vanity doors.

It may be the perspective, but to me it looks like the sink is centered.

The sink is centered over the vanity. To the left of the vanity is a built in linen tower. The cabinet door (under the sink) is open, so perhaps that is throwing it off. There is another set of drawers on that side.

How about this mirror?

Oops, I think your right. Looking at it closer I see that I completely missed that third door.

I like Beverly's choice #2 from RH best. It is the right shape and doesn't seem to compete with the rest of the items in the small space. Unless you want the mirror to make the bold statement.

Have you looked at Uttermost? They have a good selection. I like the ones with the mirrored frames, and they have a nice one with mirrored squares around the edge that might work with the squareness of your sconces and faucet. They also have this one in weathered gray wood with a little bit of curve. It's called Amedea. Don't know if it will work with everything else being so polished, but maybe it's good to add something unexpected and a softer shape for interest.

I really like the last mirror you posted. It will perfect!