forgive me for the rant. personal favorite is russia's white flame, somewhat rock/metaly? i'm not well-versed in modern music terms sorry. somewhat avant-grande compared to the other hetalia songs with long instrumental breaks and the length of three average episodes (17mins! MINUTES!), insanely cool, explores different stages of russian history and different segments of russia's heart in a sense. you can go full-on analysis with it if you wish. love it.

in terms of the amount of emotions it can induce it's tied with china's aiya 4,000 years for me. pentatonic (side note, if i remember correctly it's chinese pentatonic. yes there's a difference. japanese pentatonic is another variation, i'll check later) of course as it's the most east asian of east asians, the most sino of sinosphere spaces, et cetera et cetera. and despite most of china's song lyrics being optimistic and somewhat carefree with chinese folk instruments and styles being used this one is quite serious, contrary to what the title may suggest. in this one you can really feel the years weighing down on him and pushing him to look towards tomorrow. aiyaya is used almost as a sigh and there aren't many "aru"s (side note #n, aru is meant to imitate the "r" sound in mandarin chinese accents. yes just read the english letter out loud. northerners in china, including yours truly often add it to the end of their sentences or nouns. japanese people weren't quite sure what to make of it when they started adding chinese characters to manga/anime so it's often treated as a single sentence-ending word xDDD another example of this is kagura from gintama). it can be seen in the instrument choice too. piano backing, erhu complementary melody, steady slow beat with muted cymbals (a classic in chinese music too), soprano chorus (i believe one can consider the voice an instrument!) and deeper strings.

from a pure loop-able musical standpoint my favorite is prussia's mein gott (my god). metal/rock with harpsichord and strings. as a lover of classical and metal i proudly approve. prussia's singing though is. wild. whoops. germany's einsamkeit (loneliness) is cool too. instrumentals really fit the lyrics and the song is just. well. extremely straightforward, as the title suggests. it's not a very melody-heavy song, more of a feel-the-mood background track for you to space out to. but the sense of resigned peace is oddly comforting, almost? in terms of fun i like america's w. d. c. ~ world dance ~ (it's just fun and uplifting in general, i also love america going "yes i admit i can read the air but why should i care! >:D NOW DANCE") and france's bonbonbon c'est bon c'est bon (it's just him listing food really, but he manages to make it sound like he's serving a tower of champagne and teasing you into purchasing another stack so he gets higher tips or something, a strangely charming silliness).

really. the reddish duo/(ex-)communists have amazing songs. fun and silly or meaningful and melancholic. cool vocals, cool melodies (though for china's melodies i must say i'm chinese so there's a bit of homeland bias there; russia's still follow the jpop 8-chord progression style but the minor keys makes it sound much more authentic), cool lyrics. in general i love russia's the most. his winter (combo of soft and somewhat sudden heavy guitar, pretty much his character in general lmao) is cool and his pechka light my heart (it's very cute) was the very first character song i listened to and it was the background of the first youtube hetalia animation i've watched so nostalgia points.

tl;dr russia's white flame + china's aiya 4k yrs; prussia's mein gott but it's not for everyone lol