Pilsen and Pilsner are basically the same, as is Pilsener. Pilsen is the city in what is now Czechia, Pilsener literally means "from Pilsen", and over the years that got shortened to Pilsner. So when you see Pilsen malt or Pilsner malt, they are the same thing except each maltster will have some subtle differences. For example if you find a shop that carries actually Pilsner malt from the Czechia, it usually is slightly under modified and may require a decoction mash. Where say a Weyermann Pilsner malt is better for a single infusion mash or even a step mash.
Me personally, if I am brewing a Czech lager, I will use pilsner malt from there when I can get it. If not, I use Weyermann's Floor Malted Bohemian Pilsner malt. German lager, then it's Weyermann regular Pilsner malt, or their heirloom malt, Barke Pilsner which has a little more flavor. Weyermann other two heritage pilsner malts, Eraclea and Isaria 1924 are both great too. American style lagers, then I would use regular Weyermann over say Briess malts, but that's just my preferences.