Learn Finnish

I would not use 'laulu' when talking about contemporary music, it sounds wildly dated. Laulu also tends to refer only the vocals, or that least comes off as dismissive of the rest of the piece.

Biisi indeed works with popular music but is not appropriate for classical compositions (sävellys). Instead of 'biisi,' I would generally use 'kappale.' It does not, however, work for all pieces of art, one would not refer to a painting or a sculpture as 'kappale.'