Drop them on a table, Ultex picks sound more rigid than other materials, almost like glass. Used to like Tortex but Tortex sounds a bit rubbery compared to Ultex. 0.60mm gauge puts out the most harmonics, 0.73 a bit less but still plenty, thicker ones don't pull enough harmonics for my taste, and they feel like they bump against the string whereas 0.60's and 0.73's slide on the string with a more supple feeling.
Used 6-string "standard player" picks on my bass at the beginning but the large rounded triangle shape gives a broader grip for hitting the stronger strings on a bass. Very durable for retaining their shape, the tip seems to never wear out, but elasticity is not retained as long, so the sound loses a bit of edge after a long use. Change them when they no longer feel as flexible as new, and you're okay.