"Rarest Pokémon Spawn?"

#PokemonGO: By now there must surely be (even approximate) data or a general consensus on which Pokémon spawn is the rarest.Of course opinions will vary between players but, for example, me and my friends who play (not in the same city) seem to agree on this topic!We all agree and believe that Chansey is the rarest - We've never seen one nearby and We all play all the time.Other rares which I've read people say they've never seen (but I've caught at least 3 of each in the wild) such as Tangela, Lapras, Snorlax & Porygon are certainly rare but I don't think they're as rare.Interested to see what you guys all have to say on this - let me know your thoughts!*I edited the original post based on an astute comment - let's make this discussion about Pokémon that cannot evolve (such as the mons I listed above) via /r/TheSilphRoad http://ift.tt/2iHBr9z