MuseScore Studio plays every score with MS Basic, a small built-in soundfont, until you give it something else. Install the free MuseSounds with MuseHub and switch each instrument to them in the Mixer, and the dynamics, slurs and articulations you have already written start to change the sound.
Five Cinesamples libraries are now part of MuseSounds Pro: CineStrings, CineBrass, CineWinds, CinePerc and VOXOS Epic Choirs. Subscribers get the Cine orchestra and an epic choir for MuseScore Studio at the same price, and the subscription grows to 34 libraries.
MuseSounds Pro is the subscription for the paid MuseSounds libraries. It gives MuseScore Studio 40 partner libraries at once, from the Vienna, Spitfire, Orchestral Tools 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.