Chronologically, vintage (non-cosmair) Polo > cosmair Polo > current Polo
Modern Reserve is a separate release, a slight variation on Polo, and apparently a 'throwback' to vintage Polo.
I have tried all except vintage Polo. I don't think the cosmair version is that different from the current version of Polo green. But I'm not a vintage enthusiast, and more tolerant of reformulations than some others. The cosmair version is just a tad smoother.
I would say your best bet is to get the current version of Polo (given high price and lack of availability of the others). Terrific composition and sublime stuff, but don't go expecting best quality of ingredients (a notch below an Egoiste or a Bel Ami, but good enough). For reference, my bottle of Polo is from around 2011.
Of course, if you are a collector, get all.