If I have enough fabric I always join at an angle. If I am short on the fabric I join with a straight seam.
The theory is that the angled seam is less eye catching with most prints. Especially once quilted.
I have found this to be true with most prints but some prints show no matter what unless you take the time and effort to match it (something I won't do). Solids show no matter what style seam you use but it can be camouflaged with quilting.