All work well, and in the amounts you will need, are fairly inexpensive. The choice between them should be determined by which has the best properties given your design. Copper and vinyl tubing are available at hardware stores. Vinyl tubing and acrylic pipe are available at some pet, aquarium and garden shops. Accessories Plants can beautify a fountain in many ways.
Silk is a low maintenance choice.
Incorporating a florist's frog allows you to change the look of your fountain through foliage. And you can introduce live plants as well. Consult with your local garden shop on this last option as some plants are more fountain friendly than others. Underwater lights are sold at many of the same stores that carry pumps. Candles, floating and otherwise, also can add a dramatic element to your design.