If Fire/Ice Pokemon is picked, I'd probably be convinced to use an Ice Pokemon more than a Fire Pokemon, even if my region is in summer at the moment and would say that I should be a Fire Pokemon.
But in terms of a Pokemon I'd choose, if I absolutely have to be Fire then I'd go for Tepig. I was almost leaning towards something from Fennekin's line, but I imagine someone else would snap them up before me, plus Tepig is my second fave Unova starter.
I had the choice for an Ice-type, I definitely pick Cubchoo, Vanillite line or one of the Water/Ice Pokemon. Regardless of which type, I'd also accept being the Sunny or Snowy Castform, or even Glaceon (not as much of a Flareon fan here).