Five tracks is a very small number. There are tens of soundtracks that I love, and each one has dozens of individual themes. Asking me to just choose five... I don't know, I will always feel that I'm missing something xD
But... here goes nothing. I'll probably change my answer if a similar thread is made in the future:
Hotel Dusk: Room 215 - Bright Crystal
Pokémon HeartGold/SoulSilver - National Park
Kingdom Hearts - March Caprice for Piano and Orchestra
Xenoblade Chronicles: Definitive Edition - Zanza the Divine
Undertale - Hopes and Dreams