MuseSounds Pro is the subscription for the paid MuseSounds libraries. It gives MuseScore Studio 34 partner libraries at once, from the Vienna, Spitfire and Cinesamples orchestras to Cantai, which sings the lyrics in your score.
MuseSounds Pro gives you 34 of the paid MuseSounds libraries for a monthly or yearly fee. Buying a library, or one of the MuseSounds bundles, means paying once and keeping it. Which costs less depends on how many libraries you want and how long you will use them.
MuseHub has twelve free MuseSounds libraries for MuseScore Studio. Together they give you a full orchestra, a 40-voice choir, pianos and keyboards, guitars, harp, handbells, a marching drumline and a music box, 17.27 GB in all. They are complete libraries, they stay free, and you need a free MuseHub account to install them.
Spitfire Audio makes 11 MuseSounds libraries for MuseScore Studio, and most of them were recorded in one room, the Hall at AIR Studios in London. The four Symphony libraries, Chamber Strings and Union Chapel Organ are included in MuseSounds Pro. The other five are sold only individually.
Cinesamples makes 13 of the MuseSounds libraries on MuseHub. They include the Cine orchestra recorded at the MGM Scoring Stage in Los Angeles, solo instruments played by named artists, a choir, pianos, harps and a few rarer instruments. Five of them, the four sections of the Cine orchestra and VOXOS Epic Choirs, are in MuseSounds Pro, and the other eight you buy once and keep.