I only join as an angle in borders. In blocks I don't see a difference.

Wide borders, straight join. Narrow borders - angle join.

I much prefer angle joining for borders and sashings. They are less obvious when quilted.

Straight angle ... always.

I never join at an angle. I know the theory but I can't see that it makes a difference, frankly, and it's easier to make a straight seam.

So, I think it's a personal preference.....unless you're entering quilts in a competition which may have sewing rules.

When joining something in the middle of a strip, always Press the Seam Open, whether it is a straight or bias seam. Especially on solid colors. With the seams open, there is less chance for the light to catch on that little hump formed when seams are pressed to one side.

Flip a coin. Heads--angle, tails--butt (of course) . If you like the process and result, great. If not, you can do it differently next time. (But I'd probably be consistent within the same quilt.)

I do know from working with page layouts that the eye tends to starts in the upper right corner, and travel down and around clockwise. So if you don't want the seam to get noticed right away ,put it on the left side. If you have multiple strips joined, then stagger them.

I use Bonnie Hunter's guideline of joining borders at an angle up to about 3/5" wide, then straight. She explains why here <http://quiltville.blogspot.com/2005/06/border-hints.html>.