I don't know what range is covered by "back in the day", but my favorite arcade sound is classic Capcom, games like Ghosts 'n Goblins, Side Arms and 1943 which all used the YM2203. If this means I can vote for Capcom in general I'll place my vote.
The sound of those three games running at the same time will always be the sound of an arcade to me. The sound played such a huge part in making me a life long Capcom fan. Of course I also later discover Black Tiger, another YM2203 game, which has been my favorite arcade game ever since.