Like everything else in life, all bucktail is not created equal.
When you're at the Fly Shop, take the tail out of the package and look at the hairs. Some are nice and straight; others are wavy, like you describe. You can tie with either, but the straighter hairs look better when tyed in on the top of the hook.
If you want the best looking fiies that you can tie, then you need to be selective about the materials that you use. It's always better to see your materials in the flesh before you buy, as opposed to purchasing them online; particularly furs and feathers; not so much for synthetics.
If you think bucktail can vary, wait until you get into hackle............