Which frame/mat size would look better

[lmdbww]

I wanted to do a photo wall with DD's picture a photo of both of the dogs on either side. I'll be using Ikea Ribba frames.
www.ikea.com/us/en/catalog/products/70132525/

The dog's photos would be in 12x16 frames with 8x10 openings.

DD's photo is a 10x13 and I haven't been able to find a mat to fit it so i'll be ordering online (or getting custom made).

Should I get a 12x16 frame or a 16x20 for her photo?

(If I get the 12x16 there would be 1.75" border around all sides. If I get the 16x20 I believe the border will be more than 2" on all sides).

I cannot picture this in my head so any thoughts are appreciated.

[emjacobs]

16x20 to keep it more uniform for mat size. But take this with a grain of salt because everything that I have matted was for studio / show use so we have 4" + of mat border or an 8x10 on the top half of a 16x32.

I prefer the look of a healthy border around my photos, I feel like it really shows of the image well.

[sierramist03]

16x20 I like thicker mats

[FoxInFiji]

16x20. I like thick mats or now mats at all. Plus I like the look of a big frame with two smaller frames on either side. We have a photo collage just like that in our dining room.

[kellygordon]

16X20 would probably presented nicer.