When it comes to Pokemon cards, which one is the rarest?

I'm not a collector but I have friends who are and I was curious so I googled this. From what I saw it looks like Holo>Reverse>GX>Rainbow. Every pack has either a holo or reverse but the best reverses are harder to get. And 1 in 9 packs have a GX, and only 1% of those are rainbows. So the rainbow cards are the rarest and can sell for hundreds. Of course there are promo cards that were only given out at certain live events or in very small numbers at the pokemon store that have even higher rarity then Rainbow GXs, but its very unlikely you'll just come across those while card hunting so the four you listed should be all you have to worry about. 

Apparently it's the Pikachu Illustrator card, which someone just sold one for $195,000 and broke a world record.

I think its the No. 1 Trainer card.