I just finished the top for my queen size basket quilt. I am now ready to cut the material for the backing. I have 45" wide material that I used in the front. Do I cut and sew horizontal or vertical? Which is better? Thanks.

depending on the measurements of the quilt top, I have done my backings both ways. This latest one I am working on, I had to cut into 3 strips because it is directional fabric and I needed to have the design running up and down.

I don't think it really matters. I have done it both ways.

If I am longarm quilting it, I piece the backing horizontally. If I am not longarm quilting it, I don't worry about it.

Is there an advantage for doing it this way with longarm? I have a midarm and was curious if this is something I should think about myself?

it depends on how you are quilting it...if you are hand quilting- piece it any way you want= if you are sending it to a long-arm quilter the seams really should be horizontal- when the quilt is loaded on the frame the seam will run evenly along the rollup bar---if it is vertical it builds up layer upon layer in the center-causing wavy=saggy sides.
if you are machine quilting it on your domestic machine i think it is your choice.

you sew your backing horizontally for long-arm quilting because the quilt is loaded and rolled up on a bar---if the seam is vertical it builds up 4 layers at a time in the center of the quilt---you have a large roll-then out at the sides they are saggy-flapping everywhere--because they only have 1 layer building.
when the seam is horizontal it lays nice flat and smooth along the bar as the quilt is rolled.

thanks that makes sense! I'll definetly keep that in mind the next time I have to back a quilt for my quilting frame! :-D

many times i load my quilts on the frame sideways because it takes up less space on the take up bar (quilts are typically longer then wide) so in this case i do my pieced backing vertically.

I have done this a couple of times, but it depends on how I am quilting it.