If I had to share a list of 10 classical pieces, I would share these ones:
Holst, The Planets: Has a lot of energetic but also calming sections; there’s a reason why it was inspiration for the Star Wars scores. I particularly like the Jupiter movement but they’re all amazing
Beethoven, Symphony 5: Most people know this piece for it’s famous first movement, but the entire symphony is worth listening to. I personally prefer the second and fourth movement to the first
Mozart, Symphony 41: Mozart’s last symphony and my personal favourite, it is a perfect balance between energy and calmness, especially in the last movement. If I could, I would put at least 15 symphonies on this list but to have a balance, I’ll only include this one
Dvorak, Symphony 9, Movement 4: Highly energetic piece that has inspired many easily recognizable movie scores
Brahmns, Symphony 3: The entire symphony is good but the fourth movement is some of the best music ever made
Beethoven, Symphony 9: One of my all-time favourites, especially the fourth movement
Brahms, Symphony 4: The beginning is very sublime and calming and the end is very energetic and rejuvenating
Mendelssohn, Symphony 3: Not much to be said here except one of Chopin’s most complex pieces, technically and emotionally
Chopin, Ballade 4: Similar style to his first ballade but I personally think this piece has a stronger ending
Wagner, Tannhäuser Overture: Many pieces start energetic but I think the ones which bring the most energy have smooth transitions which this pieces demonstrates
A personal note:
Many people listen to classical music to study after they saw somewhere that it boosts memory and increases your overall spatial awareness. I believe this, but I do not listen to it for this reason. I think that people who do great research see their study as an art, and express it as such. In my work, I like seeing the complexity of ideas come together to create a simple output. Transferring this to music, classical has the difficult task of displaying emotion without words. This is primarily the reason why I think classical outperforms modern music: it is vastly more complex. Modern music can hide music behind lyrics, but classical music cannot do that. It has to tell its story somehow, so the great pieces can do that with a complex combination of intruments. When it comes time for the listener to interpret the story behind the music, it is much more subjective and challenges their imagination.