I like this song, but it also has PCM. [OPL3 + PCM] Jeroen Tel - Suske en Wiske: De Tijdtemmers - Haunted Castle (cover by Weeppiko)
I think this one is pure FM. VinsCool - Run for a Better Future (Yamaha YMF262/OPL3 Cover) (cover by SuperJet Spade)

I like the following too:
1869 (1992) Intro [Adlib, OPL2, YM3812]
https://www.youtube.com/watch?v=7NJ5Rv1ltOs

Burntime (1993) Intro [SB16, OPL3, YMF289B-S]
https://www.youtube.com/watch?v=S6TtsRH9VyA

By the way, does anyone know how the YM3420BF (OPU) compares to the YM3812 (OPL2)? The YM3420BF was installed in Yamah's PSR-36 synthesizer keyboard, for example.