From historical side I'm fan of Burgundy. I've been so even sice its introduction in AoE2. As well as Goths who don't shows up much beyond games and scenarios related to Fall of Rome. For more of fantastical stand-point I'm sucker for lizardmen, be it Homm3's Fortress, Warlord Battlecry 3 lizardmen or the ones from Total War Warhammer.
>>2413858 Seleucids or Epirus style factions. I always liked hoplites/phalanx pikemen so if I can prööööh on top of that tben I'm bound to have fun. I'm not sure what really counts as obscure though.
>>2413858 Naga. As a kid they were my favorite race in Warcraft III. They were also a neutral faction in Age of Wonders 3 where they were pretty cool except for the matriarch model which was kind of ugly.