I sew mine straight across. When I make multiple borders, I sew the different widths together, square the edges and match them up.

An important lesson for the border on a large quilt is to measure across the CENTER of your quilt and use that measurement as your border length. If your edges are not that exact size, fudge-fit the border in. If you just cut and attach without measuring, your border WILL be wavy - guaranteed.

I sew mine at a 45 degree angle just because that was the way I was taught. I'm sure either way would work.

You can do a border in many different ways. I think it is just a matter of personal choice. I usually do the sides then the top. I have only mitered one quilt and that was because of the fabric I used and I wanted to try the mitered process. Just be sure you do the border accurately so your quilt is square and easy to quilt. Many people do not know the proper way to measure for a border. Don't just pin it to the side and whack off the extra. There are many tutorials on how to measure a border. Be sure you understand the process no matter if you piece your border, use one strip or miter the corners. The best advise I can give you.

I sew mine at a 45 degree angle--how I was taught, but I try to avoid having a seam at the corner of the quilt.

When I add a border that is all the same fabric, meaning it's not a pieced design, I cut it lengthwise so there are no seams. I butt the corners with the top and bottom strips going edge to edge.

i'm confused here, are we talking about the borders or the bindings?

I sew them straight!

I cut my borders at a 45 degree angle. The fabric is not as thick when you turn it to the back and it looks neater. Good luck!

Eek! My reply was about binding. For borders that are long, I buy extra fabric so I do not have a seam within one side. Corner blocks are a good idea if you are running short!

I haven't used the 45 degree method, but a hint for matching large prints on the borders, press under your seam allowance, line up the print, and use elmers glue to hold it while you sew. I did one that came out practically invisible!