I am currently learning Russian so I would go for Latin or Classical Greek as this is pretty natural direction for Poles.
I'd say it used to be (Classical Greek and Latin). There's no wider interest now. Which I find sad, because my great-grandfather was a classical scholar.
I had German for three years in school. I don't remember anything beside "guten tag", "ich heisse" and, like every Pole, "hande hoch!"
I took 4 years of Latin, 2 years of ancient Greek, and 4 years of German in high school. My Latin has deteriorated to about 2nd-year level, the Greek to about 1st-year level, but my German is still pretty damn good since I've kept up with it.