Definitely the golden one will be the rarest, I believe. Last will be Eevee's, from what I've seen it's just stripes...
Second to last I'll give to Charizard's, although he is one of my favorites Pokemons, they really cheapened with the colors on his design and only the flame looked good.
Forth place depends on which color people prefer best, blue or red, the other will be matched with Pikachu's for second place.
^Don't think so, there are plenty of Japanese 3DS XL's that are rarer, including the Charizard 3ds xl.
You're probably right about that. I can imagine the Charizard and Eevee 3DS XL being more uncommon than the Pikachu 3DS XL, because of how exclusive the release was and being only available in Japan.
The Pikachu 3DS XL is no easy find though, I'm sure. Just recently I was talking to one of the employees at my local GameStop and he mentioned that on the day of the Pikachu 3DS XL release in the US, they had only gotten THREE in stock and were gone before the morning was over. You could find a lot of them on eBay though, but all incredibly overpriced.
Yeah, these newest ones won't be rarer, the Japanese exclusive ones will. Besides, they're Japan only, while the Pikachu got release in some other regions, and the X&Y themed got released in even more (like Australia, which is why I was able to buy one =) ). So certainly the Pikachu ones should be rarer than these new ones for that alone. Same goes for, say, Monster Hunter or Fire Emblem themed ones.