Scientific Anglers Amplitude MPX may be our favorite all-around trout line for fast-action rods. If youve watched any of our fly rod reviews, youve probably seen us casting the Amplitude MPX. This line was made to replace the GPX, SAs previous iteration of a do-it-all trout line. The MPX features more mass toward the front of the head, however, and allows anglers to access distance casting capabilities without sacrificing finesse. If youre looking for a versatile line to properly load your fast-action freshwater fly rod, youve come to the right place.